Presented  by 
Drs.  Pain  & 
Cora  Tasker* 


r   —- 

*T£C 


.^.i 

n  -.  o    -^  \-  — 


SYSTEM   OF 

PHYSIOLOGIC  THERAPEUTICS 


VOLUME  I 


System  of   Physiologic 
Therapeutics 


ELEVEN    OCTAVO  VOLUMES 

AMERICAN,   ENGLISH,   GERMAN,   AND  FRENCH  AUTHORS 


A  Practical  Exposition  of  the  Methods,  Other  than  Drug-giving,  Useful  in  the 
Prevention  of  Disease  and  in  the  Treatment  of  the  Sick.  Edited  by  SOLOMON 
SOLIS  COHEN,  A.M.,  M.D. 

Electrotherapy.      Thoroughly  Illustrated.      2  Volumes 

By  GEORGE  W.  JACOBY,  M.D.,  New  York,  with  special  articles  by  EDWARD 
JACKSON,  A.M.,  M.D.,  Denver,  Col. — By  WILLIAM  SCHEPPEGRELL,  M.D.,  New 
Orleans. — By  J.  CHALMERS  DA  COSTA,  M.D.,  Philadelphia. — By  FRANKLIN 
H.  MARTIN,  M.D.,  Chicago. — By  A.  H.  OHMANN-DUMESNIL,  M.D.,  St.  Louis. 

Climatology    and    Health    Resorts,    Including     Mineral     Springs. 

2  Volumes.      With  Colored  Maps 

By  F.  PARKES  WEBER,  M.A.,  M.D.,  F.R.C.P.,  London  ;  and  GUY  HINSDALE,  A.M., 
M.D.,  Philadelphia.  With  a  special  article  on  the  Climate  of  Hawaii,  by  DR. 
TITUS  MUNSON  COAN,  of  New  York.  The  maps  have  been  prepared  by  DR. 
W.  F.  R.  PHILLIPS,  of  the  United  States  Weather  Bureau,  Washington,  D.  C. 

Prophylaxis — Personal  Hygiene — Nursing  and  Care  of  the  Sick. 

Illustrated 

By  JOSEPH  MCFARLAND,  M.D,  Philadelphia;  HENRY  LEFFMANN,  M.D.,  Phila- 
delphia; ALBERT  ABRAMS,  A.M.,  M.D.  (University  of  Heidelberg),  San  Fran- 
cisco; and  W.  WAYNE  BABCOCK,  M.D.,  of  Philadelphia. 

Dietotherapy — Food  in  Health  and  Disease 

By  NATHAN  S.  DAVIS,  JR.,  A.M.,  M.D.,  Chicago.  With  Tables  of  Dietaries, 
Relative  Value  of  Foods,  etc. 

Mechanotherapy — Physical    Exercise.      Illustrated 

By  JOHN  KEARSLEY  MITCHELL,  M.D.,  Philadelphia;  and  LUTHER  GULICK, 
M.D.,  Brooklyn,  N.  Y.  With  a  special  article  on  Orthopedic  Appliances,  by 
DR.  JAMES  K.  YOUNG,  of  Philadelphia. 

Rest — Mental  Therapeutics — Suggestion 

By  FRANCIS  X.  DERCUM,  M.D.,  Philadelphia. 

Hydrotherapy — Thermotherapy — Phototherapy — Balneology. 
Illustrated 

By  DR.  WILHELM  WINTERNITZ,  Vienna;  assisted  by  DRS.  STRASSER  and 
BUXBAUM;  and  DR.  E.  HEINRICH  KISCH,  Prague.  Translated  by  A.  A. 
ESHNER,  M.D.,  Philadelphia.  Includes  notes  by  GUY  HINSDALE,  M.D.,  of 
Philadelphia ;  a  Chapter  on  Classification  of  Mineral  Waters,  by  DR.  A.  C. 
PEALE,  of  the  National  Museum,  Washington,  D.  C. ;  and  an  Article  on  Pho- 
totherapy, by  J.  H.  KELLOGG,  M.D.,  Battle  Creek,  Mich. 

Pneumatotherapy  and  Inhalation   Methods.      Illustrated 

By  DR.  P.  TISSIER,  Paris.    Translated  by  A.  A.  ESHNER,  M.D.,  Philadelphia. 

Serotherapy — Organotherapy — Blood-letting,    etc. — Principles    of 
Therapeutics — Digest  and  General  Index  to  all  Volumes 

By  JOSEPH  MCFARLAND,  M.D.,  Philadelphia.— O.  T.  OSBORNE,  M.D.,  New 
Haven,  Conn. — FREDERICK  A.  PACKARD,  M.D.,  Philadelphia. — THE  EDITOR, 
and  AUGUSTUS  A.  ESHNER,  M.D.,  Philadelphia. 


Descriptive  Circular  upon  Application 


A  SYSTEM 


• 


PHYSIOLOGIC  THERAPEUTICS 


A  PRACTICAL  EXPOSITION  OF  THE  METHODS,  OTHER  THAN  DRUG- 
GIVING,  USEFUL  IN  THE  TREATMENT  OF  THE  SICK 


EDITED   BY 

SOLOMON   SOLIS  COHEN,  A.M.,  M.D. 

PROFESSOR   OF   MEDICINE   AND   THERAPEUTICS   IN  THE   PHILADELPHIA    POLYCLINIC ;     LECTURER  ON 

CLINICAL   MEDICINE  AT  JEFFERSON   MEDICAL   COLLEGE;     PHYSICIAN  TO  THB 

PHILADELPHIA   AND   RUSH    HOSPITALS.    ETC. 


VOLUME  I 

ELECTROTHERAPY 

BY 

GEORGE  W.  JACOBY,  M.D. 

CONSULTING    NEUROLOGIST   TO    THR    GERMAN    HOSPITAL,    NEW   YORK    CITY  ;     TO    THB    INFIRMARY    FOR 
WOMEN  AND  CHILDREN;    AND  TO   THB   CRAIG  COLONY   FOR   EPILEPTICS,   ETC. 


IN   TWO   BOOKS 

BOOK    I 

ELECTROPHYSICS— APPARATUS    REQUIRED  FOR  THE   THERAPEUTIC  AND 
DIAGNOSTIC  USE  OF  ELECTRICITY 


"CUitb  163  Ullustrations 


PHILADELPHIA 

P.    BLAKISTON'S    SON    &    CO. 

IOI2  WALNUT  STREET 
I9O2 


V13300 


C. 


v, 


COPYRIGHT,  1901,  P.  BLAKISTON'S  SON  &  Co. 


WM.   F.   FELL  A  CO., 

ELECTROTYPER8    AND    PRINTERS, 

1330-24   SANSOM    STREET, 

PHILADELPHIA. 


THERAPEUTICS  WITHOUT  DRUGS 

A  FOREWORD  TO  THE  'SYSTEM  OF  PHYSIOLOGIC 
THERAPEUTICS' 


With  the  thorough  work  on  Electrotherapy  by  Dr.  Jacoby,  sup- 
plemented by  the  excellent  special  articles  of  Drs.  Da  Costa,  Jackson, 
Scheppegrell,  Martin,  and  Ohmann-Dumesnil,  begins  the  issuance 
of  a  series  of  volumes  treating  of  much-neglected  but  important 
remedial  measures.  It  is  a  work  that  I  have  long  had  in  mind,  and 
which,  by  a  fortunate  coincidence,  had  likewise  been  contemplated 
by  my  friend  and  publisher,  Mr.  Kenneth  M.  Blakiston.  The  system ~ 
is  the  first  of  its  kind  to  be  published  in  America  or  in  the  English 
language,  and  in  many  important  respects  differs  from  similar  works 
in  other  tongues.  Among  these  differences  are  inclusion  of  themes, 
exclusion  of  irrelevant  material,  and  general  plan.  In  its  planning, 
chiefly  based  on  my  observation  of  the  needs  and  desires  for  infor- 
mation of  students  and  practitioners,  I  have  had  the  benefit  of 
Mr.  Blakiston's  intimate  knowledge  of  medical  books,  and  in  its 
publication  the  advantage  of  his  personal  supervision  of  the  numerous 
minutiae  that  go  to  make  a  book  mechanically  perfect,  and  thereby 
diminish  the  labor  of  the  reader  in  consulting  it.  We  take  a  just 
pride  in  the  handy  form  and  clear  typography  of  the  volumes. 

Preferring  compact  books  by  single  writers  to  bulky  tomes  of  com- 
posite authorship,  I  have  endeavored  so  to  arrange  the  work  that  the 
entire  field  shall  be  covered,  that  nothing  of  moment  shall  be 
omitted,  either  from  the  general  scheme  or  from  the  special  articles, 
that  theory  and  principles  shall  be  sufficiently  but  briefly  set  forth, 
and  that  the  descriptions  of  methods,  indications,  and  counterindica- 
tions  shall  be  clear,  definite,  full,  and  practical  ;  thus  enabling  the 
general  practitioner  to  carry  out  for  himself  the  important  therapeutic 
measures  recommended,  and  to  do  so  understandingly  and  correctly. 


VI  THERAPEUTICS    WITHOUT    DRUGS 

As  the  system  is  practical  rather  than  encyclopedic,  history  has 
received  but  the  necessary  minimum  of  attention,  and  references  to 
literature  are  not  frequent. 

Each  book,  while  complete  in  itself,  also  .forms  part  of  an  organic 
whole,  and  has  been  written  and  edited  with  relation  to  its  place  in 
the  system.  Throughout  the  series  the  consideration  of  the  special 
diseases  for  which  particular  measures  are  advised  is  preceded  by  a 
general  study  of  the  physiologic  action  and  the  therapeutic  applic- 
abilities of  the  remedial  power  giving  the  book  its  title. 

In  the  concluding  volume  I  purpose  to  set  forth  the  general  prin- 
ciples of  what,  in  the  absence  of  any  better  word,  I  have  ventured 
to  term  '  Physiologic  Therapeutics '  ;  and  to  indicate  the  considera- 
tions that  should  guide  the  physician  in  the  choice  and  application 
of  the  remedial  means  discussed  in  the  special  books.  By  way  of 
preface,  however,  a  briefer  survey  of  the  field  may  be  taken,  and 
some  of  its  salient  features  pointed  out. 

Health  is  preserved,  and  when  disturbed  by  what  we  are  accus- 
tomed to  term  slight  causes,  is  obviously  restored  by  the  automatic 
mechanisms  of  the  human  body.  Life,  according  to  Mr.  Herbert 
Spencer,  is  characterized  by  the  power  of  living  beings  to  preserve 
a  mobile  equilibrium  within  their  environments,  or,  as  he  phrases  it, 
by  'the  continuous  adjustment  of  internal  relations  to  external  rela- 
tions.' In  order  that  this  equilibrium  of  the  organism  as  a  whole 
may  be  conserved,  it  is  necessary  that  there  should  be  a  like  condi- 
tion of  equilibrium  as  between  its  different  parts.  In  other  words,  a 
perfect  balance  of  function  must  be  maintained  by  continuous  adjust- 
ment of  internal  relations  to  one  another.  The  balance  of  internal 
relations,  then,  constitutes  health  ;  and  during  the  long  ages  of  evo- 
lution, the  normal  organism  has  acquired  and  developed,  to  a  high 
degree,  the  power  of  restoring  this  balance,  when  disturbed,  whether 
by  intrinsic  or  by  extrinsic  causes,  through  its  own  automatic  adjust- 
ments. Granting  the  absence  of  a  preservative  design,  we  must, 
nevertheless,  recognize  the  preservative  result  of  certain  reactions  to 
environmental  or  internal  change  ;  and  it  is  in  harmony  with  general 
biologic  doctrine  to  believe  that  favorable  variations  in  this  respect 
have  been  perpetuated  and  intensified  by  natural  selection.  A 
striking  instance  of  such  preservative  reaction  is  the  production  of 


;  '   :V  coc/  ;r 

NATURAL    RECUPERATIVE    POWER  vii 

antitoxins,  to  whose  therapeutic  utilization  we  j  ustly  point  as  among 
the  greatest  scientific  triumphs  of  the  past  century  ;  while  it  is  highly 
probable  that  allied  processes  of  immunity,  now  nearing  solution, 
and  of  which  vaccination  has  been  prophetic,  will  similarly  be  imi- 
tated by  medical  art  in  the  early  years  of  the  present  century. 

Natural  recuperative  power  has  been  developed,  not  through  the 
intaking  of  substances  foreign  to  the  organism,  but  by  physical, 
chemical,  and,  finally,  psychic  reactions  of  the  cells,  tissues,  organs, 
systems,  and — a  factor  not  to  be  ignored — of  the  organism  as  a 
whole.  Such  reactions  are  in  some  instances  simple,  in  others  com- 
plex, involving  numerous  interactions.  Nor  can  a  sharp  dividing- 
line,  either  as  to  origin  or  as  to  character,  be  drawn  between  those 
reactions  of  the  organism  to  hostile  changes  in  the  environment, 
which  we  term  morbid,  and  those  which  we  designate  as  protective, 
salutary,  or  recuperative.  As  I  have  elsewhere  said, l  not  only  must 
we  recognize  that  disease  and  recovery  are  alike  vital  processes  in 
which  the  organism  itself  is  the  most  active  agent,  and  that  neither 
morbific  nor  therapeutic  influences  endow  the  organism  with  new 
attributes  or  introduce  into  its  operations  new  powers,  but  we  must 
also  keep  in  mind  that  disease  and  recovery  are  often,  if  not  always, 
one  continuous  process.  Upon  the  discussion  of  this  intricate  sub- 
ject, however,  I  shall  not  now  enter,  but  will  merely  emphasize  the 
facts  that  a  health-preserving  and  health-restoring  tendency  exists  ; 
that  it  is  a  natural  endowment,  and  not  the  gift  of  art ;  and  that  it  is 
dependent  upon  the  inherent  properties  of  cells,  tissues,  organs,  and 
the  organism.  Some  of  these  qualities  are  constantly  manifested  (or 
kinetic),  and  in  the  normal  processes  of  recovery  are  merely  modi- 
fied— as,  for  instance,  the  thermic  reaction,  altered  in  the  pyrexia  of 
fever ;  while  others,  like  the  power  of  fibrinogenesis,  manifested  by 
blood-clotting,  are  latent  (or  potential),  and  are  evoked  only  in  reac- 
tion to  perturbing  influences.  Salutary  reactions,  however,  may  be 
delayed,  deficient,  aberrant,  or  excessive  ;  and  thus  art  must  come  to 
the  assistance  of  nature,  and  therapeusis  finds  its  reason  for  being. 
All  successful  treatment,  nevertheless,  depends  upon  the  evocation, 

1  "Some  Thoughts  Concerning  Disease  and  Recovery  in  Their  Relation  to  Thera- 
peutics." Address  before  the  Medical  and  Chirurgical  Faculty  of  Maryland,  Baltimore, 
1896. 


viii,  THERAPEUTICS    WITHOUT    DRUGS 

stimulation,  and  control  of  the  recuperative  reactions,  together  with 
the  suppression,  diminution,  or  neutralization  of  antagonistic  reac- 
tions likewise  occurring  automatically  as  the  result  of  extraneous 
morbific  influences  or  of  internal  failures  or  disturbances. 

The  means  for  accomplishing  these  therapeutic  ends  fall  into  two 
great  categories,  which  might  be  termed  '  artificial '  and  '  natural,' 
were  it  not  that  both  of  these  terms  have  certain  misleading  conno- 
tations. That  which,  for  convenience,  may  be  termed  '  artificial 
therapeutics '  consists  in  the  introduction  into  the  organism  of  sub- 
stances ordinarily  absent  therefrom  and,  mostly,  foreign  to  its  com- 
position, which,  chemically  and  otherwise,  provoke  certain  reactionary 
changes,  and  thus  modify  the  recuperative  or  the  morbific  processes. 
This  is  the  great  and  serviceable  group  of  therapeutic  means  termed 
'  drugs,'  the  use  of  which  it  is  not  my  purpose  to  antagonize  or  to 
decry.  On  the  contrary,  I  have  a  robust  faith  in  the  power  for  good 
of  the  right  drug,  given  in  the  right  dose,  at  the  right  time,  and 
equally  in  the  power  for  harm  of  the  wrong  drug,  the  wrong  dose, 
and  the  wrong  time  of  giving.  Nevertheless,  a  more  restricted  use 
may  be  made  of  drugs,  with  less  danger  of  harm-doing  by  reason 
of  mistake  in  the  election  of  drug,  dose,  or  time,  by  the  physician 
who  familiarizes  himself  with  the  powers  of  the  remedial  agents 
falling  into  the  second  group — that  of  '  natural '  or  '  physiologic  ' 
therapeutic  means. 

But  all  that  exists  in  nature  is  natural — drug  equally  with  sunlight, 
microbe  equally  with  antitoxin ;  and,  under  all  the  circumstances,  the 
disordered  functions  of  the  paralytic,  for  example,  are  equally  physio- 
logic with  the  co-ordinated  functions  of  the  athlete.  Moreover,  any 
intervention  by  the  physician  in  a  case  of  illness,  be  it  merely  to  en- 
force rest,  or  to  regulate  diet,  or  to  open  the  window  of  the  sick-room, 
is  an  exercise  of  his  art.  It  is  evident,  therefore,  that  for  the  pur- 
poses of  our  discussion  some  narrower  definition  must  be  given  to 
these  terms.  By  natural  or  physiologic  therapeutics,  then,  is  meant 
the  utilization  in  the  management  of  the  sick  of  agencies  similar  to 
those  constantly  acting  upon  the  human  body  in  health  ;  but,  because 
of  some  departure  from  health,  needing  to  be  specially  exaggerated 
or  localized  in  their  action. 

Paradoxical  though  it  may  seem,  this  limitation  of  terms  leads  to 


HABIT    AND    ENVIRONMENT  IX 

a  broader  outlook.  *  Through  it  we  are  enabled  to  find  a  firm,  scien- 
tific basis  for  hygienic  and  therapeutic  traditions  hitherto  regarded  as 
merely  empirical. 

Nor  would  I  be  misunderstood  as  decrying  empiricism.  Hippoc- 
rates, the  empiric,  was  the  father  of  scientific  medicine ;  the  dogma- 
tists were  his  opponents,  and  dogmatism  is  still  the  enemy  of  medical 
progress.  Rational  empiricism  in  medicine  consists  in  the  orderly 
arrangement  and  analysis  of  facts  observed  not  only  in  the  labora- 
tory, but  also  at  the  bedside  ;  and  in  making,  from  the  data  thus 
established,  inductions  to  the  principles  of  science  and  deductions  to 
the  applications  of  art.  In  the  experience  to  which  rational  physi- 
cians look,  must  be  included  the  whole  history  of  the  human  organism, 
and,  indeed,  so  far  as  these  can  be  learned,  a  study  of  the  con- 
ditions that  have  affected  the  living  matter  before  it  was  human  ;  for 
in  the  actions  and  reactions  of  living  matter  with  its  environment, 
from  the  simplest  to  the  most  complex,  are  to  be  found  the  in- 
fluences that  have  determined  not  alone  the  physiologic,  but  also 
the  pathologic,  development  of  man,  together  with  the  power  of  the 
organism  to  recover  from  the  disturbance  that  we  term  disease. 

Speculation  upon  the  origins  of  living  matter  is  enticing,  but  not 
profitable.  Given  the  original  living  matter  with  its  inherent  forces 
and  tendencies  and  in  its  aqueo-terraneo-atmospheric  habitat,  and  its 
development  into  man,  and  man's  coming  into  his  present  physical, 
mental,  and  moral  condition  are  the  resultants  of  habit  and  environ- 
ment. Under  these  general  heads  are  to  be  understood  the  effects 
of  climate  and  of  weather  (including  heat  and  cold,  the  physical  and 
chemical  constitution  of  the  atmosphere,  sunlight  and  other  light, 
electricity,  etc.),  the  use  of  water,  food  and  methods  of  feeding,  rest, 
and  exercise  of  function,  physical  and  mental ;  of  which  last,  not 
the  least  important  phase  is  one  commonly  overlooked — emotion. 
These  and  similar  influences  having  helped  to  make  man  what  he  is, 
may  well  be  employed  to  remake  him  when  he  departs  from  the 
norm. 

The  pathologic  influence  of  emotion  is  well  shown  in  the  evolution 
of  exophthalmic  goiter  and  in  the  protean  manifestations  of  hysteria. 
As  psychic  processes  can  share  in  the  causation  of  disease,  so  may 
they  be  utilized  to  bring  about  recovery  in  carefully  selected  cases. 


X  THERAPEUTICS    WITHOUT    DRUGS 

'  Faith  cure,'  '  mind  cure,'  '  hypnotism,'  and  the  like  have  a  basis  in 
the  fundamental  facts  of  human  nature,  and  physicians  should  study 
and  rightly  use  the  therapeutic  potency  of  suggestion,  rather  than 
suffer  charlatans  to  abuse  it. 

Pneumatotherapy  demands  more  attention  than  it  has  yet  received 
in  America.  To  refer  to  but  a  single  phase  of  its  usefulness,  I 
would  not  wish  to  undertake  the  treatment  of  many  patients  with 
pulmonary  tuberculosis,  with  asthma,  or  with  some  forms  of  chronic 
bronchitis,  were  I  to  be  deprived  of  the  use  of  compressed  and  rare- 
fied air,  though  all  the  drugs  past,  present,  and  future,  were  freely 
placed  at  my  disposal. 

Climate  has  a  vast  range  of  therapeutic  application,  by  no  means 
confined,  as  many  seem  to  think,  to  pulmonary  affections ;  but  it 
should  be  much  more  definitely  prescribed  than  is  the  common  prac- 
tice, and  with  greater  consideration  of  the  patient's  individuality  and 
of  the  numerous  details  of  daily  life  and  of  human  needs  and  desires. 
For  this  reason  much  attention  has  been  given  in  the  volume  on 
Climatotherapy  to  the  description  of  the  special  features  of  individual 
resorts. 

The  use  of  cold  water  externally  in  the  presence  of  fever  is  grow- 
ing, thanks  to  Brand,  Baruch,  and  their  disciples,  but  hydrotherapy 
has  other  and  even  more  important  applications  ;  and  while,  to  secure 
the  full  benefit  of  its  powers,  apparatus  more  or  less  elaborate  and 
special  institutes  are  needed,  and  should  be  established  by  the  pro- 
fession in  every  important  center,  much  can  be  done  at  the  patient's 
home  and  in  the  physician's  office  by  simple  means  easily  accessible. 
The  subject  of  balneology  is  partly  climatic,  partly  hydrotherapeutic, 
and  touches  also  on  drug  therapy.  It  is  much  to  be  regretted  that 
comparatively  so  few  of  the  numerous  available  springs  in  America 
have  as  yet  been  systematically  developed  ;  the  references  in  this 
section  are  of  necessity  largely  to  European  resorts. 

The  great  influence  of  diet  upon  the  human  being  in  health  and 
in  disease  warrants  the  devotion  of  a  book  to  that  topic,  and  herein 
the  important  internal  uses  of  water  are  again  emphasized. 

Recent  developments  point  to  a  wider  use  of  dry  heat,  of  sunlight, 
and  of  various  forms  of  artificial  light  and  other  radiations  in  the 
treatment  of  local  and  nutritional  disorders.  These  subjects  are 


PHYSIOLOGIC    METHODS  XI 

considered  in  appropriate  connections  ;  the  Rontgen  rays,  in  the 
volume  on  Electrotherapy. 

In  the  judicious  alternation  of  rest  and  exercise,  applicable  not 
alone  to  the  amelioration  of  neurotic  or  debilitated  states,  but  also  to 
nearly  all  metabolic  affections,  one  finds  a  method  of  treatment  in 
harmony  with  the  rhythmic  alternations  in  nature.  The  now  justly 
celebrated  'Nauheim'  or  'Schott'  methods  for  the  treatment  of  car- 
diovascular disorders  by  means  of  thermal,  saline,  and  carbonated 
baths,  and  gentle  resistance  exercises,  afford  a  combination  of  the 
advantages  of  water,  heat,  mineral  baths,  and  mechanical  measures, 
whose  striking  results  are  but  illustrations  of  what  can  be  accom- 
plished for  the  relief  even  of  patients  affected  with  serious  organic 
lesions,  without  the  use  of  drugs. 

And,  so,  examples  might  be  multiplied ;  but  sufficient  has  been 
said  to  indicate  the  wide  scope  and  the  great  power  of  the  group  of 
remedies  considered  in  the  '  System  of  Physiologic  Therapeutics ' ; 
remedies  that  have  been  employed  and  advocated,  though  perhaps 
not  always  with  sufficient  insistence,  by  the  great  teachers  of  medi- 
cine from  Hippocrates  to  our  own  contemporaries. 

But  if  the  treatment  of  disease  be  important,  its  prevention  is  even 
more  so,  and  the  measures  that  best  assist  recovery  will,  if  applied 
in  time,  best  strengthen  the  organism  to  resist  morbific  influences. 
Modern  science,  however,  goes  still  further,  and,  having  discovered 
the  exciting  causes  of  many  special  diseases  and  disorders,  as  well  as 
the  manner  of  their  transmission  and  propagation,  enables  us  to 
attempt  the  prevention  of  such  diseases  by  the  destruction  or  exclu- 
sion of  the  agents  of  infection. 

One  of  the  volumes  of  this  system  is  appropriately  devoted  to 
hygiene,  personal,  domestic,  civic,  and  national,  and  to  that  care  of 
the  sick-room  wherein  prophylaxis  and  therapeusis  meet,  if  indeed 
they  are  ever  separated. 

Professional  tradition  has  given  us  a  few  remedial  measures  upon 
the  border-line  between  medicine  and  surgery,  much  abused  in  older 
days  by  undue  employment,  much  abused  in  latter  days  by  undue 
neglect  and  vilification — blood-letting,  poulticing,  counterirritation, 
and  the  like.  Experience  proves  that  these  measures  have  a  definite 
sphere  of  usefulness,  and  they  are  treated  in  an  article  of  the  conclud- 


Xll  THERAPEUTICS    WITHOUT    DRUGS 

ing  volume  of  the  series.  Such  other  matters  as  seemed  not  of  suffi- 
cient extent  to  demand  the  devotion  of  a  separate  book  are  like- 
wise considered  in  that  volume.  There  serotherapy  and  organo- 
therapy find  place,  and  their  established  powers  and  probable  enlarged 
future  usefulness  are  set  forth.  The  digest  by  Dr.  Augustus  A. 
Eshner,  which  is  to  be  found  in  the  same  volume,  represents  but  a 
part  of  my  indebtedness  to  his  professional  and  literary  attainments 
and  friendly  counsel. 

SOLOMON  Sous  COHEN 
1525  WALNUT  STREET,  PHILADELPHIA, 
March  //, 


PREFACE 


The  number  of  existing  books  upon  electrotherapy  is  already  so 
large  that  the  need  of  another  may  be  questioned,  and  I  certainly 
should  not  have  undertaken  the  arduous  task  of  rearranging  and 
restating  well-known  facts  were  the  book  not  to  be  what  it  is,  a 
part  of  a  system  of  extra-medicinal  therapeutics. 

Electricity  certainly  merits  as  much  consideration  in  our  treat- 
ment of  disease  as  do  other  nonmedicinal  methods.  So  the  book 
had  to  be  written,  and  believing,  as  I  do,  that  there  must  be  some 
radical  defect  in  the  usual  manner  in  which  the  subject  is  presented 
to  account  for  the  generally  deplored  fact  that  medical  students  pay 
so  little  attention  to  the  study  of  electricity,  I  have  endeavored  to 
be  governed  by  the  following  considerations  : 

1.  Electricity  from  day  to  day  acquires  more  and  more  impor- 
tance scientifically  and  practically.     The  industrial  supremacy  that 
it  has  attained  is  due  to  a  thorough  knowledge  of  its  fundamental 
laws.    These  laws  must  form  the  basis  of  all  therapeutic  knowledge  ; 
yet  many  of  the  books  upon  electrotherapy  are  replete  with  errors 
and   contradictions,  while  they  are   lacking  in  precise  statements. 
A  knowledge  of  the  fundamental   laws,  the  ability  to   use  instru- 
ments in  their  application,  and  a  precise  idea  of  the  meaning  of  the 
expressions  employed,  are  therefore  essential  prerequisites  for  every 
physician  who  desires  to  utilize  electricity  as  a  remedial  agent. 

2.  The  theory  of  explanation  of  the  phenomena  observed  should 
be  the  one-fluid  theory.      This  theory  fully  explains  all  phenomena, 
is  much  simpler  than  the  two-fluid  theory,  and  is  the  only  one  that 
is  convenient  in  the  discussion  of  dynamic  electricity. 

3.  Students  of  medicine  and  physicians  in  general  evince  a  dis- 
taste for  all  mathematical  demonstrations  and  technical  explana- 
tions, and,  accordingly,  while  neither  one  nor  the  other  can  be  ne- 


XIV  PREFACE 

glected  entirely,  it  is  possible  to  simplify  them  and  reduce  them  to 
a  minimum. 

4.  Physiology  and  diagnosis  are  the  direct  supports  of  all  therapy, 
and  to  this  rule  electrotherapeutics  forms  no  exception. 

5.  In  the  employment  of  all  remedies  a  certain  degree  of  empiri- 
cism is  unavoidable  ;  perhaps  it  is  more  dominant  in  the  field  of 
electrotherapy  than  elsewhere,  and  thus  has  led  to  ultra-skepticism 
and  ultra-optimism,  both  of  which  are  deprecable.     The  more  sim- 
plified the  methods  of  treatment  become,  the  more  will  the  entire 
subject  be  denuded  of  the  mysticism  that  has  hitherto  surrounded 
it,  and  the  more  shall  we  realize  what  can  really  be  accomplished. 

References  to  literature,  and  in  many  cases  even  to  the  sources 
from  which  commonly  accepted  facts  have  been  taken,  have  been 
purposely  avoided.  A  full  tabulation  of  the  literature  of  the  sub- 
ject up  to  1895  will  be  found  in  E.  Remak's  "  Grundriss  der  Elek- 
trodiagnostik  und  Elektrotherapie." 

Much  here  presented  has  been  drawn  unreservedly  from  one  or 
more  of  the  following  sources  : 

Biggs,  C.  H.  W.,  "  First  Principles  of  Electricity  and  Magnetism," 
London,  no  date. 

Singer,  Ignatius,  and  Berens,  Lewis  H.,  "  Some  Unrecognized 
Laws  of  Nature,"  New  York,  1897. 

Stintzing,  R.,  chapter  on  the  Electrotherapy  of  Diseases  of  the 
Nervous  System,  in  "  Handbuch  der  Therapie  innerer  Krankheiten," 
Penzolt  und  Stintzing,  Jena,  1898. 

Houston,  E.  J.,  and  Kennelly,  A.  E.,  "  Electricity  in  Electro- 
therapeutics," New  York,  1898. 

Cohn,  Toby,  "  Leitfaden  der  Electrodiagnostik  und  Electro- 
therapie,"  Berlin,  1899. 

Hedley,  W.  S.,  "Current  from  the  Main,"  London,  1898. 

Laquer,  Leopold,  chapter  on  Electrotherapy  in  "  Lehrbuch  der 
allgemeinen  Therapie,"  u.s.w.,  Eulenburg  und  Samuel,  Berlin  und 
Wien,  1898. 

Other  and  older  books,  many  journal  articles,  and  various  instru- 
ment makers'  catalogues  have  been  consulted.  The  latter,  espe- 
cially those  of  W.  A.  Hirschmann,  Flemming,  Reiniger,  Gebbert, 
&  Schall,  Waite  &  Bartlett,  and  Mclntosh  Battery  Company, 


PREFACE  XV 

have  supplied  me  with  many  necessary  illustrations,  while  the  draw- 
ings for  a  large  number  of  illustrations  had  to  be  specially  made. 

The  growing  importance,  as  a  source  of  electricity  for  medical 
work,  of  the  currents  supplied  to  modern  houses  for  light  and 
power,  warrants  the  somewhat  extended  consideration  given  to  the 
methods  by  which  these  currents  may  be  utilized  with  safety. 

The  book,  all  in  all,  will  serve  as  a  guide  for  further  study,  yet 
chiefly,  I  hope,  as  an  incentive  to  practical  work,  for  it  is  my  belief 
that  from  no  book  can  the  employment  of  electricity  be  learned 
satisfactorily. 

No  one  can  be  more  cognizant  of  the  defects  of  the  book  than 
am  I,  but  I  feel  certain  that  these  defects  will  be  least  emphasized 
by  those  who  have,  at  some  time,  been  called  upon  to  perform  a 
similar  work. 

GEORGE  W.  JACOBY 

605  MADISON  AVENUE,  NEW  YORK, 
September  i,  igoo. 


PART  I— ELECTROPHYSICS 

CHAPTER   I  PAGE 

FUNDAMENTAL  CONCEPTIONS,      !7~33 

Electric  Vibrations.  Correlation  of  Energy.  The  One-fluid  Theory. 
Unity  of  Electricity.  Excitation.  Friction.  Contact.  Attraction  and 
Repulsion.  Positive  and  Negative.  Conduction.  Insulation.  Density. 
Tension.  Influence.  Quantity.  Electrometer.  Potential.  Capacity. 
Condensation.  Electromotive  Force.  Methods  of  Producing  Electricity. 

CHAPTER   II 

FRICTIONAL  (STATIC)  ELECTRICITY,     34-44 

Friction  Machines.  Cylinders.  Plates.  The  Electrophorus.  Influence 
Machines.  Condensers.  Fulminating  Pane.  Leyden  Jar. 

CHAPTER   III 

DYNAMIC  ELECTRICITY, 45~7i 

Chemical  Generators.  Galvanism.  Voltaic  Pile.  Current.  Circuit. 
Cells.  Elements.  Electrolyte.  Various  Forms  of  Cells.  Battery. 
Positive  and  Negative  Plates.  Poles.  Current  Direction.  Pressure. 
Resistance.  Ohm's  Law.  Arrangement  of  Cells. 

CHAPTER    IV 

EFFECTS  OF  THE  ELECTRIC  CURRENT, 72-94 

Physical,  Chemical,  and  Physiologic  Effects.  Electrolysis.  Polarization. 
Electromagnetic  Effects.  Magnetic  Field.  Electric  Osmosis.  Thermic 
Action.  Induction.  Measurement.  Voltameter.  Ammeter.  Voltmeter. 
Resistance  Coils.  Wheatstone  Bridge.  Ohmmeter. 

CHAPTER   V 

OTHER  METHODS  OF  OBTAINING  AND  ALTERING  ELECTROMOTIVE  FORCE,   .    95-104 
Dynamic  Induction.    Magnetic  Induction.    Volta-magnetic  Induction  Appa- 
ratus.     Dynamos.     Thermo-electricity.     Thermopile.     Sinusoidal  Current. 

CHAPTER  VI 

VARIETIES  OF  ELECTROMOTIVE  FORCE, 105-116 

Continuous.  Alternating.  Pulsating.  Steady.  Symmetric.  Dissym- 
metric. Intermittent.  Nonintermittent.  Sinusoidal.  Nonsinusoidal. 
High  Frequency. 


XV111  CONTENTS 


PART    II— APPARATUS    REQUIRED   FOR   THE 

THERAPEUTIC   AND    DIAGNOSTIC   USE 

OF    ELECTRICITY 

CHAPTER   I  PAGE 

FRICTIONAL  ELECTRIC  APPARATUS  AND  ITS  USE, 120-135 

Influence  Machines.  Charge  and  Recharge.  Care  of  the  Machine.  Attach- 
ments. Insulator.  Electrodes.  Leyden  Jars.  Chains.  Methods  of 
Application.  Indirect  Spark.  Direct  Spark.  Static  Shock.  Static  In- 
sulation. Static  Breeze.  Static  Induced  Current.  Determination  of 
Polarity. 

CHAPTER    II 

GALVANIC  APPARATUS  AND  ITS  USE, 136-170 

Source.  Batteries.  Dynamos.  Regulators.  Selectors.  Rheostats.  Volt 
Controllers.  Arrangement  of  Resistance  in  Circuit.  Reversers.  Inter- 
rupters. Combiners.  Measurement.  Milliamperemeters.  Voltmeters. 
Electrodes.  Cords. 

CHAPTER    III 

SOURCES  OF  CURRENT  SUPPLY  FOR  DIAGNOSTIC  AND  THERAPEUTIC  PURPOSES, 

AND  THE  APPARATUS  NECESSARY  FOR  ITS  USE,         171-189 

Requirements  of  Stationary  and  Portable  Batteries.  Different  Types  of 
Cells.  Pole  Testers.  Care  of  Apparatus.  Causes  and  Remedies  of 
Disorder.  Currents  from  Central  Stations.  Direct  and  Alternating  Cur- 
rents. Dangers  of  High  Voltage  Currents.  Leakage  Currents.  Controll- 
ing Apparatus.  Transformed  Systems.  Breakdown  of  Insulation.  Safe- 
guards. Sudden  Increase  of  Current.  Compound  Shunt.  Method  of 
Using  Street  Currents.  Limit  Resistance.  Rheostat.  Author's  Method. 

CHAPTER    IV 

APPARATUS  FOR  ALTERING  ELECTROMOTIVE  FORCE, 190-209 

Induced  or  Faradaic  Currents.  Magneto-electric  Machines.  Volta-mag- 
netic  Machines.  Dubois-Reymond  Coils.  Faradimeter.  Standard  Coils. 
Current  Source.  Sinusoidal  Currents  and  Apparatus.  Apparatus  for 
High  Frequency  Currents.  Hydro-electric  Baths.  Cautery  Apparatus. 
Transformer.  Commutator.  Storage  Cells.  Exploring  Lamps. 

CHAPTER    V 

RONTGEN  RAYS  OR  X-RAYS,   ...  210-227 

Production  of  X-rays.  Characteristics.  Properties.  Source.  Geissler 
Tube.  Crookes  Tube.  Kathode  Rays.  Antikathode.  Focus  Tubes. 
Adjustable  Vacuum  Tubes.  Excitation  by  Influence  Machine.  Excita- 
tion by  Ruhmkorff  Coil.  Condenser.  Interrupter.  Fluoroscope.  Ski- 
agraphy.  Radiographic  Table.  Localization  Methods.  X-Ray  Burns. 


LIST  OF  ILLUSTRATIONS 


1.  Analysis  of  Solar  Light  by  a  Prism,  Showing  the  Heat,  Light,  and  Actinic 

Areas  of  the  Spectrum, 18 

2.  Electrification  of  Pith  Balls,  ...                 .....'            20 

3.  Sphere  Showing  the  Accumulation  of  Electricity  on  its  Surface, 25 

4.  Ovoid  Showing  Distribution  of  Electricity, 25 

5.  Showing  the  Action  of  an  Electrified  Isolated  Conductor  upon  a  Nonelectri- 

fied  Isolated  Conductor,                 26 

6.  Showing  Electrification  by  Influence, 27 

7.  Gold-leaf  Electroscope, 28 

8.  Electrometer,        28 

9.  Simple  Glass  Plate  Machine, 35 

10.  Ramsden's  Machine, 36 

11.  Cylinder  Machine, 37 

12.  The  Electrophorus,      38 

13.  Holtz  Machine,        ...        .            .    .  39 

14.  Diagram  Showing  the  Principle  of  the  Holtz  Machine, 40 

15.  Wimshurst  Machine,        42 

1 6.  Metal  Plate  Condenser,      43 

17.  Condenser, 44 

1 8.  Condenser, 44 

19.  Leyden  or  Kleist  Jar, 44 

20.  Voltaic  Pile,                   46 

21.  Simplest  Form  of  Cell,        47 

22.  Daniel  Cell, 49 

23.  Gravity  Cell, 50 

24.  Gravity  Cell, 50 

25.  Grove  Cell,  .    .                50 

26.  Bunsen  Cell  and  its  Component  Parts, 51 

27.  Grenet  Cell,       .    .                     52 

28.  Original  LeclanchS  Cell, 54 

29.  Leclanche  Cell  Without  Porous  Cup, 54 

30.  Modified  Leclanche  Cell, 54 

31.  Law  Telephone  Cell,           55 

32.  Silver  Chlorid  Cell, 55 

33.  Showing  the  Flow  of  Current  from  Positive  to  Negative  Plate,  and  from  Posi- 

tive to  Negative  Pole,  ...                .        .    .                56 

34.  Showing  Variations  in  Water  Pressure, 5& 

35.  Showing  a  Simple  Circuit  Containing  Three  Equal  Resistance  Wires,      ...  60 

36.  Showing  a  Simple  Circuit  Containing  One  Resistance  Wire, 6l 

37.  Showing  a  Simple  Circuit  Containing  Two  Resistance  Wires  in  Series,     ...  61 

38.  Showing  a  Simple  Circuit  Containing  Two  Resistance  Wires  in  Parallel,     .    .  62 

39.  Showing  Two  Resistance  Wires  Placed  in  Parallel, 65 

40.  Showing  the  Principle  of  the  Shunt  as  Applied  to  Water,      66 

41.  Showing  the  Principle  of  the  Shunt  as  Applied  to  Electricity, 67 

42.  Cells  Arranged  in  Series, 69 

43.  Cells  Arranged  in  Parallel,      .         .             70 

44.  Diagram  of  Cells  Arranged  in  Parallel, 71 

45.  Illustrating  Ampere's  Rule  of  the  Deflection  of  a  Magnetic  Needle,    ....  74 


XX  LIST    OF    ILLUSTRATIONS 


46.  Illustrating  Ampere's  Rule  of  the  Deflection  of  a  Magnetic  Needle,  ....  74 

47.  Illustrating  Ampere's  Rule  of  the  Deflection  of  a  Magnetic  Needle,    ....  74 

48.  A  Voltameter,       77 

49.  Showing  the  Principle  of  the  Multiplicator,          79 

50.  An  Astatic  System  of  Needles,  .        .            80 

51.  Showing  the  Method  of  Winding  Coil  in  the  Original  Form  of  Astatic  Gal- 

vanometer,                  So 

52.  Showing  the  Method  of  Winding  Coil  in  Improved  Form  of  Astatic  Galva- 

nometer,        81 

53.  Scale  of  Mirror  Galvanometer, 82 

54.  Showing  Course  of  Deflected  Ray  on  Scale  of  Mirror  Galvanometer,  ....  82 

55.  Showing  Principle  of  the  Ammeter, 84 

56.  Ammeter,      84 

56  A.  Arrangement  of  Ammeter  Needle, 84 

57.  Showing  how  the  Ammeter  Needle  is  Mounted, 85 

58.  Weston's  Ammeter,  Showing  Working  Parts, 86 

59.  Weston's  Ammeter  Complete,    ....            .                86 

60.  Showing  the  Relation  of  Pressure  to  Outflow  in  a  Water  Tank,       88 

61.  Weston's  Voltmeter, 89 

62.  Construction  of  Resistance  Coils, 91 

63.  Arrangement  of  Resistance  Coils, 92 

64.  Showing  Method  of  Determining  Unknown  Resistances  by  Substitution,     .    .  92 

65.  Showing  Method  of  Determining  Unknown  Resistances  by  the  Wheatstone 

Bridge,        ....        93 

66.  Showing  the  Method  of  Determining  Unknown  Resistances  By  Means  of  an 

Ammeter  and  a  Voltmeter,       94 

67.  Showing  the  Method  of  Producing  an  Induced  Current, 96 

68.  An  Induction  Coil,               97 

69.  Faraday's  Magneto-electric  Machine, 99 

70.  The  Horseshoe  Inductor, loo 

71.  Thermo-electric  Couple, 102 

72.  Thermopile,  .    .            102 

73.  The  Noe  Thermopile, 103 

74.  Graphic  Representation  of  a  Continuous  Electromotive  Force, 106 

75.  Graphic  Representation  of  the  Electromotive  Force  Produced  by  a  Continuous 

Current  Dynamo,       107 

76.  Graphic  Representation  of  a  Pulsatory  Electromotive  Force, 107 

77.  Graphic  Representation  of  an  Intermittent  Electromotive  Force, 108 

78.  Graphic  Representation  of  an  Alternating  Electromotive  Force, 109 

79.  Graphic  Representation  of  a  Gradually  Alternating  Electromotive  Force,    .    .  109 

80.  Graphic  Representation  of  a  Gradually  Alternating  Electromotive  Force,    .    .  no 

81.  Graphic  Representation  of  a  Gradually  Alternating  Electromotive  Force,    .    .  no 

82.  Graphic  Representation  of  a  Symmetric  Electromotive  Force, in 

83.  Graphic  Representation  of  a  Dissymmetric  Electromotive  Force, 112 

84.  Graphic  Representation  of  a  Sinusoidal  Electromotive  Force, 112 

85.  Graphic  Representation   of  a  Pulsatory  Electromotive  Force, 113 

86  and  87.  Showing  the  Oscillations  of  a  Liquid  in  the  Limbs  of  a  U-Tube,     .    .  115 

88.  Scheme  of  Herz's  Induction  Coil  for  Producing  High  Frequency  Oscillations,  116 

89.  Holtz-Toeppler  Machine  (Hirschtnann,  Berlin], 121 

90.  Holtz-Toeppler.  Machine  (  Waite  &  Bartlett,  New  York}, 122 

91.  Glaeser's  Cylinder  Machine  {Vienna},          .  123 

92.  Electrodes  and   Accessories   for   Static  Machine   ( Waite  &°  Bartlett,  New 

York}, 126 

93.  Method  of  Applying  the  Indirect  Spark, 128 

94.  Method  of  Applying  the  Direct  Spark,     . 129 

95.  Method  of  Applying  the  Leyden  jar  Spark, 130 

96.  Morton's  Spark  Electrode, 131 

97.  Roller  Electrode,      131 

98.  Concentrator  and  Stand,      132 


LIST    OF    ILLUSTRATIONS  XXI 


99.   Method  of  Producing  the  Static  Induced  Current, 133 

100.  Morton's  Pistol  Electrode,          133 

101.  Rider  Cell  Selector, 139 

102.  Combined  Cell  Selector,      140 

103.  Riders  of  Combined  Cell  Selector, 141 

104.  Gaiffe's  Cell  Selector, 141 

105.  Showing  Regulation  of  Current  by  Resistance  in  Shunt, 143 

106.  Graphite  Pencil  Rheostat, 144 

107.  Modified  Graphite  Rheostat, 145 

108.  Modified  Graphite  Rheostat, 145 

109.  Vetter  Rheostat, • .  146 

no.  Working  Parts  of  Vetter  Rheostat 146 

in.   Fluid  Rheostat,                 147 

112.  Improved  Fluid  Rheostat, .    .  148 

113.  Showing  Method  of  Regulation  of  Current  by  Placing  Resistance  in  Circuit,  .  156 

114.  Showing  a  Rheostat  Placed  in  Circuit,      151 

115.  Showing  a  Rheostat  Placed  in  Shunt, 152 

116.  Commutator, 154 

117.  Galvano-faradaic  Combiner,             155 

1 18.  Front  View  of  Upright  Milliamperemeter, 158 

119.  Showing  Tension  Spring  of  Milliamperemeter, 158 

120.  Another  Form  of  Upright  Milliamperemeter, 159 

121.  Horizontal  Milliamperemeter, 160 

122.  Jewell  Voltmeter, 162 

123.  Electrode  Handlef 163 

123  A.   Electrode  Handle, 163 

124.  Varieties  of  Electrodes, 164 

124  A.   Interrupting  Handle  and  Various  Electrodes, 165 

124  B.  Abdominal  and  Other  Pads.     Aural  Electrode, 166 

125.  Wire  Brush  Electrode, - 166 

126.  Unpolarizable  Electrode, 167 

127.  Combination  Electrode  Handle 168 

128.  Interrupting  Electrode  Handle,  .    .            168 

129.  Pole-changing  and  Current-controlling  Handle, 169 

130.  Electrode  with  Hard-rubber  Spring  Attachment, 169 

131.  Electrode  with  Elastic  Belt  Attachment, 169 

132.  Pole  Tester, '. 176 

133.  Pole  Tester, ....  176 

134.  Diagram  Showing  the  Arrangement  of  Wires  in  the  200  Volt  Circuit,      .    .    .  182 

135.  Diagram  Showing  the  Danger   of  the  Three-wire  System, 183 

136.  Diagram  Showing  Where  the  Controlling  Apparatus  Should  be  Placed  in 

Order  to  Avoid  Danger,   .    .                 184 

137.  Diagram  Showing  How  the  Current  is  Derived  from  a  Double  Shunt  Circuit,  .  185 

138.  Magneto-electric  Machine,  ...                190 

139.  Showing  Circuit  Breaker  and  its  Connections 192 

140.  The  Neef  or  Wagner  Hammer, 192 

141.  Dubois-Reymond  Coil, 194 

142.  Magneto-generator  for  Developing  a  Sinusoidal  Current, 199 

143.  An  Alternator  for  Generating  a  Current  of  the  Sinusoidal  Type,       199 

144.  Apparatus  for  Obtaining  a  High  Frequency  Current, 201 

145.  Simple  Form  of  Electric  Bath-tub,                 203 

146.  Handle  and  Various  Electric  Cautery  Ends, 204 

147.  Set  of  Miniature  Exploring  Lamps, 207 

148.  Lamp  for  Using  Reflected  Light, 208 

149.  The  Wappler  Electric  Controller, 208 

150.  Showing  the  Course  Taken  by  an  Electric  Discharge  in  a  Crookes  Tube,    .    .  212 

151.  An  X-ray  Tube,                 ...             213 

152.  Focus  Tube  with  Adjustable  Vacuum, 214 

153.  Queen  Self-regulating  X-ray  Tube, 215 


XX11  LIST    OF    ILLUSTRATIONS 


154.  Automatic  Adjustable  Vacuum  X-ray  Tube,  for  use  with  Alternating  Currents,  215 

155.  Showing  the  Attachment  of  X-ray  Tube  to  Static  Machine,       21 6 

156.  Edison  Instantaneous  Air-break  Wheel, 218 

157.  Fluoroscope,          219 

158.  A  Skiagram, ...         .  221 

159.  Skiagram  of  Aneurysm  of  the  Transverse  Arch  of  the  Aorta  (Plate  by  Pro- 
fessor Arthur  Goodspeed,  from  a  case  of  Dr.  S,  Solis- Cohen's),                       .    .  222 

160.  Leonard's  Polyclinic    ("Queen")    Radiographic   Table.       Examination  of 

Thorax  with  Fluoroscope, ....                              .        .  224 

161.  Leonard's  Polyclinic  ("Queen")  Radiographic  Table.     Insertion  of  Plate,  .  225 

162.  Localization  Apparatus,       .        226 

163.  Sweet's  Appliance  for  Localizing  Foreign  Bodies  in  the  Eye, 227 


A  SYSTEM  OF  PHYSIOLOGIC  THERAPEUTICS 


ELECTROTHERAPY— BOOK  I 


PART  I 
ELECTROPHYSICS 


A  SYSTEM  OF  PHYSIOLOGIC  THERAPEUTICS 


ELECTROTHERAPY 


PART  I 
ELECTROPHYSICS 

CHAPTER  I 
FUNDAMENTAL    CONCEPTIONS 

Electric  Vibrations.  Correlation  of  Energy.  The  One-fluid  Theory. 
Unity  of  Electricity.  Excitation.  Friction.  Contact.  Attraction  and 
Repulsion.  Positive  and  Negative.  Conduction.  Insulation.  Density. 
Tension.  Influence.  Quantity.  Electrometer.  Potential.  Capacity. 
Condensation.  Electromotive  Force.  Methods  of  Producing  Electricity. 

Our  conceptions  of  the  nature  of  electricity  are  very  obscure, 
and  we  are  to  a  large  extent  in  ignorance  concerning  it.  We  know 
that  what  we  call  electricity  will  decompose  water,  heat  a  wire 
through  which  it  flows,  deflect  the  compass  needle  from  its  north- 
south  position  of  rest,  and  that  each  time  we  interrupt  the  flow  of 
electricity  at  any  place  a  spark  is  produced  ;  but  what  it  is  that 
causes  these  effects  we  do  not  know.  This  ignorance  is  due  to  a 
certain  extent  to  our  forced  endeavor  to  consider  electricity  as  an 
entity — as  a  distinct  form  of  energy. 

If,  however,  we  would  but    look  upon  electricity  simply  as  a 

further  manifestation  of  natural  force  developed  through  molecular 

motion,  we  should  at  any  rate  obtain  a  less  hazy  idea  of  its  nature. 

Nevertheless,  we  should  still  be  in  the  region  of  hypothesis,  rather 

2  17 


i8 


FUNDAMENTAL    CONCEPTIONS 


than  in  that  of  demonstration.      In  short,  our  knowledge  of  elec- 
tricity is  obtained  from  its  effects  alone. 

At  present  we  know,  through  Mayer's  and  Joule's  demonstrations, 
that  chemism,  heat,  and  light,  the  three  great  forces  of  nature,  are 
directly  interchangeable  as  to  direction  and  rapidity  of  the  molecular 
vibrations.  This  is  easily  demonstrated  in  regard  to  light  and  heat 
by  a  piece  of  metal  the  temperature  of  which  is  being  raised.  At 
first  the  vibrations  caused  by  the  heated  metal  are  slow  and  in  a 
vertical  direction ;  as  they  become  more  rapid,  the  metal  appears 
to  give  out  light  or,  as  we  commonly  say,  becomes  red-hot.  As 
the  heat  is  increased,  the  molecular  vibrations  become  still  more 
rapid  ;  and  in  part  changing  their  direction  from  vertical  to  horizontal, 
produce  a  white  or  bluish  light,  which  indicates  the  so-called  white 
heat. 


FIG.  i. — ANALYSIS  OF  SOLAR  LIGHT  BY  A  PRISM,  SHOWING  THE  HEAT,  LIGHT, 
AND  ACTINIC  AREAS  OF  THE  SPECTRUM. 


Now,  this  progressive  change  cannot  fail  to  remind  us  of  the 
solar  spectrum  ;  here  also  we  have  the  color  varying  from  red  to 
the  deep  blue  or  violet.  This,  however,  is  only  the  visible  spec- 
trum. In  the  analysis  of  solar  light  by  a  prism  we  get  three  dis- 
tinct and  separate  areas,  as  shown  in  figure  I. 

First  there  is  the  central  or  visible  portion  of  the  spectrum, 
which  begins  with  the  dark  red  and  ends  with  the  ultra-violet. 
This  is,  however,  really  the  smallest  portion  of  the  spectrum. 
Above  the  violet,  extends  an  invisible  area  three  times  the  length  of 
the  visible  portion,  which  is  significant  on  account  of  its  power  to 
bring  about  chemical  action  ;  while  below  the  red,  an  area  in  which 
heat  is  developed  extends  ten  times  the  length  of  the  visible  spec- 


MOLECULAR    VIBRATIONS  19 

trum.  For  convenience  we  speak  of  the  thermic,  luminous, 
and  actinic  rays  of  the  spectrum,  and  these  merge  so  closely  one 
into  the  other  that  it  is  difficult  to  define  their  limits.  It  has  always 
been  easy  to  reproduce  the  heat  and  the  light  areas  of  the  spectrum ; 
but  of  the  ultra-violet  or  chemical  area,  although  recognized,  little 
was  understood  until  recently,  when,  through  the  discovery  of 
Rontgen,  this  portion  of  the  spectrum  has  been  reproduced  in  the 
X-ray.  Thus  we  have  light  proper  as  an  intermediary  between 
heat  and  the  so-called  X-ray,  and  these  three  forces  are  all  recog- 
nizable by  their  effects  only.  So,  too,  electricity  is  known  from  its 
effects  alone,  and  these  effects  are  interchangeable,  so  that  under 
certain  conditions  we  can  derive  from  them  heat,  light,  and  chemi- 
cal action.  It  would  not  be  going  too  far,  therefore,  to  consider 
electricity  as  a  form  of  molecular  vibration,  and  add  it  to  make  a 
series  with  our  other  natural  forces.  In  the  order  of  the  rapidity  of 
vibration  our  new  table  would  read :  heat,  light,  X-rays  (or 
chemism),  and  electricity. 

A  few  fundamental  experiments  will  also  teach  us  that:  (i) 
The  electric  state  is  one  of  relativity  only  ;  (2)  electricity  is  due  to 
the  equalization  that  takes  place  between  two  bodies  in  different 
degrees  of  excitation  ;  (3)  the  excitation  of  such  bodies  differs 
only  in  degree  and  not  in  kind. 

While  our  conception  of  the  nature  of  electricity  may  be  con- 
sidered assumptive  and  theoretic,  we  are  by  no  means  lacking  in 
positive  knowledge  concerning  its  actions  and  the  laws  that  govern 
them.  On  the  contrary,  our  knowledge  in  these  directions  is  so 
precise  and  extensive  that  it  may  be  questioned  whether  there  is 
any  probability  of  its  being  broadened.  Let  us,  therefore,  begin 
our  investigation  of  the  therapeutic  possibilities  and  uses  of  electri- 
city with  a  study  of  these  effects  and  laws  ;  confining  ourselves  for 
the  most  part  to  positive  knowledge,  but  making  use  of  theory 
whenever  it  will  render  the  facts  more  easily  comprehensible. 

The  earliest  ideas  of  electricity  were  derived  from  the  effects 
observed  when  one  substance  was  rubbed  against  another,  and  in 
order,  therefore,  to  gain  a  knowledge  of  the  effects  upon  which  our 
assumption  of  electricity  is  based,  let  us  take  up  the  earliest  evi- 
dences that  we  are  pleased  to  call  electric. 


2O 


FUNDAMENTAL    CONCEPTIONS 


Phenomena  of  Electrification. 

Excitation. — We  all  know  that  when  certain  substances,  such 
as  amber,  glass,  sulphur,  hard  rubber,  are  rubbed  with  some  other 
substance, — as,  for  instance,  a  piece  of  silk, — both  substances  ac- 
quire the  property  of  attracting  light  bodies,  such  as  shreds  of  paper, 
when  brought  near  to  them.  The  rubbed  substances  are  said  to 
be  electrified,  and  the  property  that  thus  becomes  manifest  and 
whose  cause  is  unknown  is  called  electrification. 

This  property  may  also  be  acquired  by  placing  a  nonelectrified 
body  in  contact  with  an  electrified  one  ;  it  may  then  easily  be  seen 
that  the  previously  electrified  body  has  lost  part  of  its  electrification, 
inasmuch  as  it  attracts  light  bodies  with  less  force.  Electrifica- 


FIG.  2. — ELECTRIFICATION  OF  PITH  BALLS. 

tion  is  best  studied  as  follows  :  Take  three  glass  standards  (Fig.  2) 
bent  in  the  shape  of  a  Roman  "  f,"  and  fixed  in  wooden  or  metal 
bases.  We  will  call  them  I,  2,  3.  From  I  and  2  suspend  single 
small  balls  of  elder  pith  by  fine  silk  threads,  so  that  they  hang  per- 
fectly free,  and  from  3  suspend  in  the  same  way  two  balls  so  that 
they  touch  each  other.  In  addition  to  this  take  a  rod  of  glass  a 
few  inches  long,  a  stick  of  sealing-wax,  and  a  piece  of  silk.  If  we 
rub  the  glass  or  sealing-wax  briskly  with  the  silk  and  hold  it  close 
to  the  ball  of  No.  I,  the  ball  will  be  attracted  to  the  rod  ;  but  so 
soon  as  it  has  touched  the  rod,  it  will  be  repelled.  Rub  the  rod 
again  and  hold  it  to  the  pair  of  balls  of  No.  3,  and  they  will  be 
attracted  as  was  the  single  ball,  and  on  removing  the  rod  after  the 


CONDUCTORS    AND    INSULATORS  21 

balls  have  touched  it,  they  will  come  to  rest ;  not,  however,  resum- 
ing their  position  of  contact,  but  standing  off  at  a  distance  from  each 
other.  Bring  No.  i  and  No.  2  near  each  other.  Touch  No.  I  with 
the  rubbed  glass  rod  and  No.  2  with  the  rubbed  sealing-wax.  The 
two  balls  will  now  attract  each  other,  but  if  they  are  allowed  to 
touch,  they  will  fall  apart  again  and  lose  all  sign  of  electrification. 

These  phenomena  are  designated  as  electric,  and  the  agent 
producing  them  is  termed  electricity.  How  this  agent  should 
be  looked  upon  we  have  seen,  but  there  are,  as  will  be  shown 
later,  certain  conveniences  in  speaking  of  it  as  a  f  1  u  i  d,  and  so  long 
as  we  know  that  this  term  is  used  merely  for  the  purpose  of  com- 
parison and  continue  to  bear  this  in  mind,  there  can  be  no  objection 
to  its  use. 

Conduction. — When  a  scrap  of  paper  is  attracted  to  a  rubbed 
rod  of  glass  and  remains  attached  to  it,  this  scrap  acquires  the 
power  of  attracting  a  second  piece,  this  in  turn  of  attracting  a  third, 
and  so  on.  The  electric  state  has  therefore  been  conducted  from 
the  first  scrap  to  the  second,  from  the  second  to  the  third,  etc.  In 
certain  substances  it  will  also  be  found  that  by  both  methods  of 
electrification,  friction  as  well  as  contact,  the  acquired  property  may 
remain  localized  at  the  point  rubbed  or  touched,  or  it  may 
spread  over  the  entire  surface  of  the  body.  Hence  bodies 
have  been  classified  as  good  or  bad  conductors  of  electricity, 
as,  analogously,  bodies  may  be  good  or  bad  conductors  of  heat. 

If  we  examine  the  various  substances  as  to  their  power  of  con- 
ducting electricity,  we  shall  find  many — for  instance  all  metals — 
that  are  such  good  conductors  that  they  at  once  discharge  their 
electricity,  while  others  are  such  poor  conductors  that  they  entirely 
oppose  the  spread  of  electricity  ;  the  latter  are  called  n  o  n  c  o  n- 
ductors  or  insulators.  Such  are  the  resins,  oils,  etc.  Between 
the  two  classes,  conductors  and  insulators,  there  exists  a  class  of 
semiconductors  that  require  more  or  less  time  in  order  to  con- 
duct electricity.  Dry  air  is  a  good  insulator  :  as  the  moisture  of  air 
increases,  its  conductivity  increases.  This  difference  in  the  conduc- 
tivity of  various  substances  explains  why  certain  substances — as, 
for  instance,  metals — cannot  be  electrified  unless  certain  precautions 
are  taken  ;  for  if  they  are  held  directly  in  the  hand,  the  electricity 


22  FUNDAMENTAL    CONCEPTIONS 

produced  in  them  is  at  once  conducted  through  the  body  of  the 
operator  to  the  earth,  where  it  is  spread  over  an  infinitely  large 
surface  and  is  lost.  For  this  reason  the  earth  may  be  looked  upon 
as  a  large  reservoir,  and  every  body  that  is  placed  in  a  state  of 
good  conduction  with  the  earth  will  lose  its  electricity,  while  if  it  is 
placed  in  a  state  of  bad  conduction,  by  interposing  a  bad  conductor 
between  the  electrified  body  and  the  earth,  the  electricity  will  be 
retained.  If,  therefore,  we  desire  to  retain  the  electricity  upon  a 
conductor  for  a  time, — as,  for  instance,  upon  a  hollow  ball, — we 
must  insulate  the  ball  by  attaching  it  to  a  bad  conductor,  as  a 
glass  or  resin  rod,  and,  furthermore,  endeavor  to  have  the  sur- 
rounding air  as  dry  as  possible.  Thus  poor  conductors  are  utilized 
to  insulate  good  ones  ;  but  it  must  not  be  forgotten  that  no  con- 
ductor or  insulator  is  perfect. 

Every  insulated  body  may  be  electrified  by  friction  as  well  as  by 
contact.  There  are  also  other  ways  of  effecting  electrification  besides 
those  of  rubbing  dissimilar  substances  together  or  placing  dissimilar 
substances  in  contact  directly.  Those  most  used  are  by  making 
the  contact  of  dissimilar  substances  through  an  intermediary,  as  by 
placing  these  substances  in  a  liquid  ;  by  warming  or  cooling  the 
junction  of  two  dissimilar  substances  ;  by  making  changes  in  a 
system  of  magnets  and  wires,  either  the  strength  of  the  magnet 
or  the  relative  position  of  the  magnets  and  wires  being  altered. 

Unity  of  Electricity. 

No  matter  how  produced,  electricity  shows  the  same  qualities, 
although  these  may  differ  quantitatively.  There  is  but  one  elec- 
tricity. Whether  we  produce  it  through  the  friction  of  dissimilar 
substances  (frictional  electricity),  or  by  the  immersion  of 
two  dissimilar  substances  in  a  fluid  (galvanic  electricity),  or 
by  soldering  two  pieces  of  different  metals  together  at  two  different 
places  and  then  heating  or  cooling  one  metal  (thermo-elec- 
tricity), or  if  we  effect  the  changes  previously  spoken  of  in  the 
system  of  magnets  and  wires  (magneto-electricity),  the  elec- 
tricity is  always  one,  and  its  actions  are  always  the  same.  Of 
these  actions  we  shall  speak  later  ;  let  us  confine  ourselves  for  the 
present  to  the  effects  already  observed  in  our  pith-ball  experiments, 


THE    ONE-FLUID    THEORY  23 

in  order,  if  possible,  to  explain  the  theory  of  the  nature  of  the  force 
that  produces  these  effects. 

The  theory  of  Symmer,  which  assumes  the  existence  of  two 
electric  fluida  and  explains  all  the  electric  phenomena  by  the 
assumption  that  an  attraction  takes  place  between  the  molecules 
of  these  electric  fluida  and  the  molecules  of  matter,  similar  electric 
molecules  repelling  each  other,  dissimilar  ones  attracting  each  other, 
but  in  both  cases  dragging  away  with  them  the  molecules  of  matter, 
has  been  abandoned  by  electricians  ;  yet,  strange  to  say,  it  has  been 
retained  by  nearly  all  writers  on  medical  electricity.  The  two-fluid 
theory  must  give  way  to  the  one-fluid  theory  of  Franklin,  to  the 
elucidation  of  which  we  shall  confine  ourselves. 

We  must  accept  the  fact  that  electricity  exists  in  all  bodies,  in 
space,  and  in  the  earth,  its  quantity  being  determined  in  each 
case  by  the  circumstances  under  which  it  is  found.  The  constant 
quantity  may  be  considered  as  a  standard  or  normal  quantum  of 
electricity.  As  the  result  of  certain  interactions  with  other  bodies, 
a  particular  body  may  contain  more  or  less  electricity  than  this 
normal  quantum.  In  the  first  case  we  say  the  body  has  a  plus  of 
electricity,  or  is  positively  electrified;  in  the  second  case,  that 
it  has  a  minus  of  electricity,  or  is  negatively  electrified.  These 
differences  correspond  to  the  various  modes  of  electrification  that  we 
have  already  described.  Arbitrarily  we  assume  that  the  glass  that 
has  been  rubbed  with  the  piece  of  silk  has  been  positively  electri- 
fied. As  a  matter  of  fact,  it  is  totally  immaterial  whether  we 
assume  that  it  has  received  a  plus  or  a  minus  of  electricity,  for  this 
"  more"  or  "less"  is  simply  relative  to  the  quantity  of  electricity 
contained  in  the  surrounding  objects. 

Furthermore,  we  must  recognize  that  electricity  seems  to  move 
with  facility  in  certain  bodies  that  we  have  designated  as  good  con- 
ductors, while  in  those  that  are  bad  conductors  its  movement  meets 
with  a  great  resistance  or  opposition.  Also  must  we  admit  that 
electricity  seems  to  have  an  effect  on  electricity  at  a  distance,  the 
action  being  similar  to  attraction  and  repulsion.  Of  course,  we  do 
not  actually  acknowledge  action  at  a  distance.  We  must  imagine 
that  the  presence  of  electricity  at  a  certain  point  in  some  way 
modifies  the  surrounding  medium,  which,  thus  altered  from  particle 


24  FUNDAMENTAL    CONCEPTIONS 

to  particle,  in  its  turn  acts  upon  the  electricity  placed  at  some  other 
point.  This  being  understood,  we  may  suppress  the  intermediary 
vehicle  and  reason  as  though  we  had  an  action  at  a  distance. 

By  this  hypothesis  the  general  facts  can  easily  be  explained.  If 
a  body  contains  the  normal  quantity  of  electricity,  no  action  will 
be  noticed  in  the  neighborhood  of  this  body.  If,  however,  its  elec- 
tric content  be  altered,  then  such  alteration  will  also  change  the 
reciprocal  actions  of  the  electricity  contained  in  the  body,  of  that 
in  the  surrounding  medium,  and  of  that  in  neighboring  bodies. 
This  change  may  be  effected  in  various  ways : 

1.  By  some  action,  mechanical,  calorific,  or  chemical,  between 
two  nonelectrified  bodies.    One  of  the  bodies  thus  receives  more 
electricity  than  it  had  and  becomes  positively  electrified  ;  this,  how- 
ever, can  occur  only  if  the  other  body  loses  electricity  and  becomes 
negatively  electrified  ;  in  other  words,  the  bodies  under  such  circum- 
stances become  electrified   oppositely. 

2.  A  nonelectrified  body  is  brought  in  contact  with  a  body  elec- 
trified positively  or  negatively  (plus  or  minus)  ;  in  the  first  instance 
the  electrified  body  gives  up  a  part  of  its  electricity  in   order  to 
arrive  at  a  state  of  equilibrium  ;  it  becomes  less  completely  elec- 
trified, but  the  other  gains  what  this  one  loses,  and  consequently 
it  must  become  electrified  positively.     The  process  is  reversed  in 
the  opposite  case.     Thus  the  charge  is  always  of  the  same  sign 
as  that  of  the  charging  body. 

Attraction  and  repulsion,  which  are  exerted  between  bodies  with 
contrary  or  similar  electrification,  may  also  be  explained  satis- 
factorily by  this  one-fluid  theory ;  the  essential  is  that  the  bodies 
are  differently  charged — that  is,  that  they  contain  different  quan- 
tities of  electricity ;  and  such  attraction  of  unlikes  or  repulsion  of 
likes  will  be  proportional  to  the  quantities  of  electricity  present. 

Density  or  Distribution  of  Electricity. — Electricity  gathers 
on  the  surface  of  objects,  as  can  be  seen  from  the  following 
simple  experiments.  Take  an  insulated  brass  ball,  such  as  A 
(Fig.  3),  that  has  a  metal  covering,  C,  fitted  carefully  around  it, 
but  in  two  halves,  so  that  it  may  conveniently  be  removed  by  means 
of  the  insulating  handles,  B,  B.  Place  the  covers  over  the  ball,  and 


DENSITY 


charge  the  whole  apparatus  with  electricity.  Then  remove  the 
covers  C,  C,  and  all  of  the  charge  will  be  found  upon  them,  while 
the  ball  A  will  have  no  charge  whatever ;  thus  showing  that  the 
whole  charge  was  distributed  over  the  surface. 


FIG.  3. — SPHERE  SHOWING  THE  ACCUMULATION  OF  ELECTRICITY  ON  ITS  SURFACE. 

Since  electricity  distributes  itself  over  the  surface  of  a  body,  the 
same  quantity  of  electricity  distributed  over  a  small  surface  will 
necessarily  be  more  dense,  more  compact,  than  if  spread  over  a 
large  surface.  Thus  upon  a  sphere  the  density  will  be  equal  at  all 


FIG.  4. — OVOID  SHOWING  DISTRIBUTION  OF  ELECTRICITY. 

points,  while  upon  an  ellipsoid  the  density  varies  at  the  different 
points.  In  figure  4  the  greatest  density  would  be  found  at  "a," 
the  least  at  "b,"  and  an  intermediary  state  of  density  at  "c." 


26 


FUNDAMENTAL    CONCEPTIONS 


The  greater  the  density  of  electricity,  the  greater  will  be  its 
tension — that  is,  the  tendency  of  electricity  to  overcome  the 
resistance  of  the  air,  until  finally,  this  resistance  being  overcome, 
the  electricity  escapes.  If  the  escape  occurs  in  the  dark,  it 
appears  luminous. 

Electrification  by  Influence. 

Induction. — When  an  electrified  body  is  placed  in  the  vicinity 
of  other  bodies,  insulated  or  not,  it  sets  up  in  these  other  bodies 
electric  modifications — i.  e.,  variations  in  the  distribution  of  elec- 
tricity;  thus  it  acts  upon  them  by  influence. 


+C 


FIG.  5. — SHOWING  THE  ACTION  OF  AN  ELECTRIFIED  ISOLATED  CONDUCTOR  UPON  A 
NONELECTRIFIED  ISOLATED  CONDUCTOR. 

While  it,  however,  is  influencing  the  other  bodies  it  is  also  being 
influenced — its  repartition  of  electricity  is  being  altered.  We  are 
dealing  with  the  distribution  of  electricity  in  a  system  of  neighbor- 
ing bodies.  Thus  we  have  (Fig.  5)  an  isolated  conductor,  B  c,  and 
a  ball,  A,  positively  electrified,  which  we  approach  to  a  certain  dis- 
tance of  each  other.  The  equilibrium  existing  in  the  body  B  c  will 
be  disturbed,  and  on  account  of  the  repulsion  exercised  by  A  there 
will  be  produced  a  movement  of  electricity  from  B  toward  c,  thus 
causing  a  deficit  at  B  and  a  surplus  at  c.  There  will  thus  be  at  the 
point  of  the  conductor  nearest  to  the  influencing  body  a  contrary 


INFLUENCE 


charge  to  that  of  this  body,  and  at  the  most  distant  part  a  similar 
charge.  This  phenomenon  is  sometimes  termed  induction. 

The  result  would  be  analogous  if,  instead  of  a  positively  charged 
body,  A,  we  were  dealing  with  one  negatively  charged.  If  A  is 
removed  or  discharged,  eveiy  action  of  influence  ceases  immediately, 
and  B  c  returns  to  its  primary  unelectrified  state. 

Charging  by  Influence. — If  B  C  (Fig.  6),  instead  of  being  insu- 
lated, is  in  communication  with  the  earth,  the  effect  exercised  by  A 
will  be  the  same  in  a  general  way,  but  on  account  of  the  connection 
with  the  common  reservoir,  the  earth,  the  only  demonstrable  change 
will  be  that  at  B,  which  will  be  opposite  and  contrary  to  A.  In  this 


FIG.  6. — SHOWING  ELECTRIFICATION  BY  INFLUENCE. 

case  die  charge  at  B  is  greater  than  in  the  former  experiment.  If  A 
is  now  removed  or  discharged,  the  body  B  C  will  return  to  its  un- 
electrified state.  If,  however,  before  so  removing  the  body  A  the 
communication  between  B  C  and  the  earth  is  broken,  the  former 
(B  C)  will  retain  the  charge  that  it  had  acquired  in  consequence  of 
the  action  of  A. 

This  fact  is  very  important,  for  we  thus  have  another  mode  of  pro- 
ducing electrification  ;  and  it  will  be  noted  that,  contrary  to  electri- 
fication by  contact,  here  the  conductor  B  C  receives  an  opposite 
charge  to  that  of  A,  while  A  suffers  no  modification  of  its  own 
charge. 


28 


FUNDAMENTAL    CONCEPTIONS 


The  attraction  and  repulsion  of  light  bodies  are  dependent  for 
the  most  part  upon  this  influence  action,  and  the  phenomenon  repre- 
sents the  endeavor  of  the  bodies  to  regain  and  maintain  their  electric 
equilibrium.  If  two  bodies  are  dissimilarly  charged,  they 
try  to  approach  each  other  in  order  to  neutralize  themselves,  and 
thus  apparently  attract  each  other.  If,  however,  they  are  simi- 
larly charged,  they  separate  in  order  to  prevent  their  condition 
becoming  one  of  more  unstable  equilibrium  by  a  higher  charge. 
This  is  repulsion. 

These  phenomena  of  influence  are  manifested  in  the  mode  of  action 


FIG.  7. — GOLD-LEAF  ELECTROSCOPE. 


FIG.  8. — ELECTROMETER. 


of  the  electroscope,  an  apparatus  employed  for  the  purpose  of  dis- 
covering whether  a  body  is  electrified,  and  determining  the  (-f-  or — ) 
nature  of  its  charge.  The  gold-leaf  electroscope  is  most  used  (Fig.  7). 
It  consists  of  two  narrow  strips  of  gold-leaf  pasted  to  the  end  of 
a  metal  rod,  the  other  end  of  which  is  so  fastened  into  the  cupola 
of  a  bell  glass  that  it  passes  through  the  glass  to  the  outside  and 
ends  in  a  free  knob.  The  gold-leaf  strips  hang  free  in  the  center 
of  the  glass.  The  bell  glass  not  only  protects  the  gold-leaf  strips 
from  currents  of  air,  but  also  directly  insulates  them  against  sur- 
rounding objects.  If  the  knob  of  such  an  electroscope  is  touched 
by  an  electrified  body,  the  strips  of  gold-leaf  diverge. 


POTENTIAL  29 

A  modified  electroscope  serving  for  the  measurement  of  the 
quantity  of  electricity  is  called  an  electrometer  (Fig.  8). 

Charge. — In  any  electrified  body  there  is  a  certain  amount  of 
electricity  that  can  thus  be  measured,  and  this  we  call  its  quan- 
tity, or  charge  of  electricity.  It  must  be  borne  in  mind  that 
whether  the  charge  be  large  or  small  in  a  given  body  depends 
solely  on  the  quantity  of  electricity,  and  not  on  the  size  of  the 
body.  Thus,  two  bodies  of  different  sizes  having  the  same  charge 
have  each  exactly  the  same  quantity  of  electricity,  and  not  differ- 
ing quantities  proportional  to  their  size. 

Potential. — Two  bodies  are  said  to  be  of  the  same  potential 
if,  when  connected  by  a  wire  conductor,  no  modification  of  their 
electric  condition  takes  place.  If  such  a  modification  does  take 
place,  they  are  said  to  be  of  different  potential,  and  by  agreement 
the  body  that  gives  up  its  electricity  is  said  to  be  of  a  higher  poten- 
tial than  the  body  that  receives  it.  For  purposes  of  comparison  the 
earth  is  considered  to  be  of  zero  potential,  and  all  bodies  from 
which  the  electricity  flows  to  the  earth,  or,  in  other  words,  that 
when  connected  with  the  earth  lose  electricity,  are  said  to  be  of  a 
positive  potential ;  while,  on  the  other  hand,  all  bodies  to  which 
electricity  flows  from  the  earth,  or  that  gain  electricity  when  con- 
nected with  the  earth,  are  of  a  negative  potential.  Hence  the 
potential  of  a  body,  irrespective  of  the  size  or  nature  of  the  body,  is 
its  degree  of  electrification  above  or  below  that  of  the 
earth.  A  practical  conception  of  these  facts  may  be  obtained  by 
instituting  a  comparison  between  electricity  and  water.  Thus,  if 
we  wish  to  produce  a  flow  of  water  from  one  point  to  another,  we 
must  make  the  point  frojn  which  the  water  is  to  flow,  higher 
than  the  point  to  which  it  is  to  flow.  It  will  be  seen  that  potential 
is  not  the  same  as  quantity. 

Capacity. — The  electric  capacity  of  a  body  may  be  considered 
to  be  the  greatest  quantity  of  electricity  that  may  be  acquired  by 
that  conductor.  The  same  quantity  of  electricity  communicated  to 
different  bodies  does  not  necessarily  bring  them  to  the  same  poten- 
tial ;  different  bodies  have  a  different  electric  capacity,  and  we  may 
have  a  large  electric  capacity  and  yet  a  very  low  potential,  and 
vice  versa.  This  capacity  may  be  gauged  by  dividing  the  quantity 


3<D  FUNDAMENTAL    CONCEPTIONS 

of  electricity  given  up  to  a  body  by  the  variation  in  potential  that 
it  has  undergone  ;  thus,  if  C  equal  capacity,  Q  equal  quantity,  and 
V  equal  variation  in  potential,  then  C  =  y. 

The  capacity  of  a  body  depends  not  only  upon  the  surface  of  the 
body,  but  also  upon  those  bodies  that  are  in  its  immediate  vicinity. 

Charging  and  Discharging. 

As  already  stated,  when  a  body  is  electrified,  it  is  said  to  receive 
a  charge  of  electricity,  or,  more  briefly,  to  be  charged. 

Charging  consists  in  a  disturbance  of  the  normal  elec- 
tric equilibrium  of  the  body  charged,  which  thus  passes  into  a 
state  of  higher  or  lower  potential .  If  the  potential  be  raised, 
the  body  is  said  to  have  received  a  positive  charge,  and  if  the 
potential  be  lowered,  the  charge  is  termed  negative.1 

The  electrified  body  is  thus  in  a  condition  to  manifest  electro- 
motive force  under  favorable  circumstances  by  discharging 
itself  of  its  electric  tension,  and  returning  to  its  former  state 
of  equilibrium. 

Discharge  may  be  partial  or  complete,  sudden  or  pro- 
longed. A  charged  body  may  yield  up  at  once  its  entire  excess 
of  electricity,  and  thus  become  nonelectrified  ;  or  it  may  yield  up 
this  excess  (or  charge)  in  successive  portions,  and  thus  become  by 
degrees  less  and  less  electrified,  until  finally  it  becomes  neutral  again. 

Only  insulated  conductors  can  receive  and  retain  charges. 
If  an  insulated  conductor  charged  with  electricity  be  approximated 
to  an  insulated  conductor  not  so  charged,  influence  becomes 
established,  and  contrary  states  of  electric  potential  manifest 
themselves  at  the  points  of  the  conductors  that  are  nearest  to 
each  other  ;  the  nearer  the  conductors  are  brought  together,  the 
more  does  the  one  influence  the  other,  and  thus  the  greater  will  be 
the  tendency  to  equalization ;  this  tendency  to  equalization,  or 


1  It  may  do  no  harm  to  repeat  here,  what  has  been  said  before,  that  the  terms  "  high  " 
and  "low,"  "positive"  and  "negative,"  are  relative  and  arbitrary ;  and  that  although 
the  terminology  and  hypotheses  of  the  one-fluid  theory  have  been  adopted  throughout  this 
book  for  the  sake  of  clearness  and  simplicity,  the  author  and  the  editor  both  regard  electric 
energy  as  the  analogue  of  light  energy  and  of  heat  energy,  and  therefore  as  the  con- 
comitant of  a  special  mode  of  molecular  motion. 


CHARGING    AND    DISCHARGING  3! 

tension,  may  become  so  strong  as  to  overcome  the  resistance  fur- 
nished by  the  intermediary  body  of  air,  and  a  discharge  takes 
place,  accompanied  by  the  phenomena  of  manifest  heat  and  light. 

If  the  charge  of  the  electrified  conductor  be  susceptible  to 
instantaneous  and  continuous  renewal,  there  will  be  a 
constant  and  steady  equalization,  manifested  by  a  series  of  rapidly 
succeeding  sparks,  known  as  the  voltaic  arc;  but  if  the 
charge  be  not  so  renewed,  or  be  renewed  but  slowly,  the  results  will 
vary  in  accordance  with  the  shape  of  the  conductors  and  the  resist- 
ance that  the  air  interposes. 

Should  one  or  both  of  the  conductors  be  pointed,  electric 
equilibrium  will  become  established  slowly;  but  if  no  such  point 
exists,  the  return  to  equilibrium  is  sudden,  manifests  itself  by  a 
spark,  and  is  known  as  a  disruptive  discharge. 

In  the  first  case,  if  one  of  the  conductors  be  pointed  and  its 
electric  tension  becomes  very  great,  equalization  soon  sets  in  and 
continues  until  an  equilibrium  with  the  surrounding  bodies  has 
been  established.  This  phenomenon  takes  place  gradually,  and  is 
accompanied  by  manifest  light,  which,  however,  can  be  observed 
only  when  other  light  is  excluded.  This  form  of  discharge  is 
known  as  the  convective  discharge,  or  electric  spray. 

On  the  other  hand,  if  the  conductors  have  no  point,  but  the 
distance  between  them  be  sufficiently  small,  the  electric  discharge 
will  be  sudden,  and  the  equalization  will  take  place  in  the  form  of  a 
spark  ;  and  this  spark  will  be  manifested  by  a  zigzag  line  of  light, 
accompanied  by  a  more  or  less  sharp  noise  or  crepitation,  and 
requiring  but  an  incalculably  short  time  for  its  transmission  between 
the  conductors. 

The  intensity  of  the  electric  spark  depends  upon  the  quantity 
of  electricity.  When  this  is  great,  the  effects  may  be  enormous, 
as  is  evidenced  in  the  discharge  of  an  electric  cloud  ;  here  the  mani- 
fest light  of  the  spark  is  called  lightning,  while  the  noise  or 
crepitation  is  known  as  thunder. 

Conductive  Discharge. — We  have  seen  what  takes  place  be- 
tween two  bodies  in  unstable  electric  equilibrium  when  brought 
near  to  each  other  but  still  withheld  from  actual  contact  by  the  in- 
terposition of  a  nonconducting  medium  or  dielectric  (usu- 


3  2  FUNDAMENTAL    CONCEPTIONS 

ally  the  air)  across  or  through  which  influence  (induction)  is  mani- 
fested. If,  now,  these  two  bodies  be  connected  by  a  conductor, 
the  equalization  of  potential  from  the  charged  body  to  the 
uncharged  one  will  take  place  along  the  conductor,  and  a 
current  will  pass.  The  current  will  continue  to  pass  along  the 
conductor  so  long  as  the  charged  body  continues  to  give  up  elec- 
tricity to  the  uncharged  body,  or  until  an  electric  equilibrium  has 
been  established.  When  one  body  discharges  its  electricity  to 
another  body  through  a  conductor,  as  just  described,  the  process 
is  known  as  a  conductive  discharge. 
Condensation  of  Electricity. 

When  an  insulated  body  is  connected  by  a  wire  with  any  source 
that  furnishes  electricity  at  a  certain  potential,  the  body  will  become 
charged  until  it  has  attained  the  same  potential  as  the  source ;  the 
quantity  it  receives  depending  upon  its  capacity.  When  an  equil- 
ibrium has  been  established,  the  body  is  said  to  be  completely 
charged.  If,  now,  another  conductor  that  is  in  connection  with  the 
earth  is  brought  near  this  charged  body,  the  potential  of  the  charged 
body  will  become  lessened,  so  that  if  it  is  again  placed  in  contact 
with  the  source  of  electricity,  it  will  receive  an  additional  charge 
before  a  state  of  equilibrium  becomes  again  established  through  its 
having  again  attained  the  potential  of  the  source.  By  the  near 
presence  of  a  grounded  conductor  the  capacity  of  the  body  has 
been  increased,  or,  what  is  the  same,  the  quantity  of  electricity 
necessary  to  charge  the  body  completely  is  greater  now  than  it  was 
in  the  beginning.  It  is  therefore  said  that  here  electricity  has  been 
condensed,  or  that  we  have  effected  a  condensation  of  electricity. 
Electromotive  Force. 

There  is  an  inherent  force  that  starts  the  current  of  electricity 
and  maintains  it;  this  is  really  the  effect  of  the  difference  of 
potential  between  two  bodies.  No  machine — and  we  refer  to 
the  friction  machine  as  the  one  with  which  the  student  is  most 
familiar — produces  electricity  directly,  but  simply  effects  a  difference 
in  potential  and  thus  gives  rise  to  a  force  that  will  be  manifested  as 
tension  or,  under  suitable  conditions,  exerted  in  the  production  of 
an  electric  current.  It  is  a  force  that  tends  to  set  electricity 
in  motion,  and  is  therefore  called  electromotive  force  (E  M  F). 


ELECTROMOTIVE    FORCE  33 

Tension,  potential,  and  electromotive  force  are  thus 
closely  related  terms  ;  tension  referring  to  the  state  of  the  hypo- 
thetic electric  fluid  and  potential  to  the  relation  between  electrified 
bodies,  due  to  the  greater  or  less  tension  under  which  their  con- 
tained electricity  exists  ;  this  in  turn  depending  upon  the  relative 
strength  of  the  forces  tending  to  move  it  and  to  oppose  its  motion. 
Thus,  electromotive  force  bears  the  same  relation  to  electricity  that 
pressure  does  to  water;  and  similarly  as  we  speak  of  negative 
pressure  in  the  case  of  a  vacuum  pump  or  negative  quanti- 
ties in  mathematics,  so  we  speak  of  negative  potential  or 
negative  charge  in  the  case  of  certain  electric  phenomena.  It 
will  be  necessary  to  refer  again  to  these  terms  and  to  consider  the 
designation  pressure  in  a  more  detailed  manner. 

No  electric  action  can  be  produced  without  a  prior  production  of 
electromotive  force,  and  this  force  will  produce  electric  action  under 
favorable  conditions,  while  under  unfavorable  ones  it  will  not.  An 
electromotive  force  may  practically  be  produced  for  medical  pur- 
poses in  three  different  ways  : 

1.  By  the  action  of  mechanical  energy  (frictional  machine, 
electrostatic  induction  machine,  dynamo-electric  machine). 

2.  By  the  action  of  radiant  heat  (thermo-electric  cell). 

3.  By  chemical  action  (voltaic  or  primary  cell,  charged  stor- 
age or  secondary  cell). 

As  the  character  of  the  electromotive  force  may  be  variously 
altered,  and  as  such  alterations  play  an  important  part  in  the  use 
of  electricity  in  diagnosis  as  well  as  in  therapeutics,  it  will  be  more 
practical  to  study  the  methods  of  production  of  electromotive  force, 
together  with  the  laws  that  govern  the  flow  of  current,  and  then  to 
treat,  purely  arbitrarily — 

1.  Frictional  machines — frictional  electricity. 

2.  Galvanic  or.  primary  cells — g  a  1  v a  n  i  s  m . 

3.  Induction  machine — induced  or  faradaic  electricity. 

4.  Thermo-electric  machine — thermo-electricity. 

After  we  have  considered  the  foregoing,  we  shall  be  able  better 
to  understand  the  alterations  of  electricity — viz.  (i)  currents  of 
high  frequency  and  (2)  sinusoidal  currents  and  apparatus. 
3 


CHAPTER  II 
FRICTIONAL  (STATIC)  ELECTRICITY 

Friction  Machines.      Cylinders.     Plates.      The  Electrophorus.     Influence 
Machines.      Condensers.     Fulminating  Pane.     Ley  den  Jar. 

Electricity  produced  by  friction  maybe  obtained  through  a  num- 
ber of  devices.  Such  a  device,  as  first  constructed  by  Otto  von 
Guericke,  represents  the  earliest  friction  machine.  This  con- 
sisted of  a  sphere  of  sulphur,  which  was  rotated  and  against  which 
the  hands  were  applied ;  a  metal  chain  suspended  from  the  ceiling 
by  insulating  silk  cords  formed  the  conductor  upon  which  the  elec- 
tricity was  gathered. 

Later,  in  1708,  Hawksbee  substituted  a  glass  globe  for  the 
sulphur  sphere,  and  Bose,  in  1745,  made  use  of  silk  to  rub  the 
glass.  Next  a  cylinder  of  glass  rubbed  by  a  cushion  was  employed, 
and  finally  a  plate  of  glass  was  substituted  for  the  cylinder.  Such 
a  simple  plate  machine  is  shown  in  figure  9. 

Here  a  plate,  G,  is  made  to  revolve  between  two  insulated  up- 
rights, A,  B  ;  a  third  upright,  c,  carries  a  rubber  made  of  leather  and 
amalgam,  which  presses  against  the  glass  plate  when  this  is  revolved 
by  means  of  a  crank  handle.  Another  upright,  D,  carries  a  con- 
ductor, E,  to  the  end  of  which,  nearest  the  glass  plate,  are  attached 
two  combs,  one  on  each  side  of  the  plate.  The  leather  cushion  of 
the  upright,  c,  is  now  grounded  by  means  of  a  chain.  When  the 
glass  plate  is  revolved,  both  the  amalgamated  cushion  and  the  glass 
plate  become  electrified.  The  cushion,  however,  being  in  connec- 
tion with  the  earth  and  thus  a  part  of  it,  will  be  raised  only  to  the 
potential  of  the  earth  ;  while  the  glass  will  be  brought  to  a  higher 
potential — that  is,  receive  a  plus  of  electricity,  or  become  posi- 
tive. On  account  of  the  slight  conductivity  of  the  glass,  this  plus 
of  electricity  will  not  spread  over  the  surface  of  the  plate,  but  will 
remain  at  the  point  where  it  is  produced  until,  by  revolution  of  the 

34 


PLATE    MACHINES 


35 


plate,  it  is  brought  opposite  to  the  points  of  the  combs,  where  it 
will  be  collected  and  will  flow  into  the  conductor,  E.  The  plate 
being  freed  from  electricity,  will  again  become  electrified  when  the 
other  half  passes  between  the  cushions.  Thus  the  circle  is  kept 
up,  electricity  accumulating  on  the  conductor,  E,  and  the  quan- 
tity increasing  until  the  loss  of  electricity  through  the  air,  which 
loss  also  augments  equally  with  the  charge,  is  exactly  equal  to 
the  quantity  furnished  ;  then  a  condition  of  equilibrium  will  have 
been  established.  The  necessity  of  establishing  the  connection 
between  the  rubber  and  the  earth  is  easily  understood ;  for  were 
the  cushion  insulated,  only  a  single  charge  could  be  obtained  and 


FIG.  9. — SIMPLE  GLASS  PLATE  MACHINE. 

no  accumulation  of  charges  could  result.  To  energize  the  action 
of  the  cushion  its  surface  is  covered  with  tin  bisulphate,  or  an 
amalgam  of  zinc,  tin,  bismuth,  and  mercury.  It  is,  however,  not 
sufficient  merely  to  produce  a  large  quantity  of  electricity,  but  loss 
must  be  guarded  against.  In  order  to  do  so,  the  surrounding  air 
must  be  kept  as  dry  as  possible,  the  plate  and  its  support  being  well 
insulated  and  kept  free  from  moisture,  and  a  special  provision,  as 
shown  in  the  accompanying  illustration  of  Ramsden's  machine  of 
1766  (Fig.  10),  still  further  diminishes  the  loss  from  the  plate.  For 
this  purpose  sectors  of  silk  are  so  fastened  to  the  framework  of  the 


7O  FRICTIONAL    ELECTRICITY 

*/ 

machine  that  they  cover,  without  touching,  two  quadrants  of  the 
disk,  and  thus  oppose  the  loss  through  the  air. 

In  figure  II  a  cylinder  machine  is  shown.  Here  the  conduc- 
tor carries  the  rubber  that  covers  a  part  of  the  cylinder.  If  the  one 
conductor  is  connected  with  the  earth,  the  other  will  become  raised 
to  a  higher  potential  and  will  be  positive,  so  that  the  current  will 
flow  over  the  air  gap  from  plus  to  minus.  By  reversing  the  con- 
nections with  the  earth  the  current  may  be  reversed. 


FIG.  10. — RAMSDEN'S  MACHINE. 


Before  explaining  the  construction  and  action  of  another  class  of 
electric  machines  it  will  be  necessary  to  describe  the  electrophorus, 
as  these  machines  depend  for  their  action  not  so  much  upon  fric- 
tion as  upon  influence. 

The  electrophorus,  invented  by  Volta,  is  an  apparatus  for  the 
repeated  utilization  of  electricity  during  a  longer  time,  after  a  single 
excitation,  and  consists  of  a  cake  of  resin,  hardened  in  a  circular 


CYLINDER    MACHINE 


37 


metallic  plate,  and  a  cover,  constituted  by  a  disk  of  metal  to  which 
is  attached  an  insulating  handle  of  wood  or  glass. 

In  figure  12,  A  represents  the  shellac  plate  in  its  metal  covering, 
D.  B  represents  the  metal  plate  with  its  insulating  rod,  C.  In 
order  to  obtain  charges  we  must  first  electrify  the  shellac  plate  by 
rubbing  it  with  a  piece  of  catskin.  Then  the  plate  is  negatively 
charged.  One  gently  places  the  metal  disk  B  on  the  charged  plate 
A,  and  grounds  the  upper  surface  of  the  disk  by  placing  the  finger 
on  it  ;  on  withdrawing  the  finger  and  removing  the  disk  by  means 
of  the  rod  C,  we  shall  find  that  the  disk  is  positively  charged  with 


FIG.  ii. — CYLINDER  MACHINE. 


electricity.  This  can  be  discharged  and  the  experiment  repeated 
with  a  like  result.  It  is  essential  that  the  metal  covering  of  the 
plate  be  in  connection  with  the  ground.  If  this  condition  is  not 
observed,  we  shall  find  that  very  shortly  we  get  no  further  charge. 
The  phenomenon  of  the  electrophorus  is  dependent  on  the  prin- 
ciple of  induction,  as  explained  on  page  27.  In  order,  however, 
to  understand  the  mechanism,  the  plate  A  must  be  regarded  as 
consisting  of  three  parts  instead  of  two.  The  shellac  itself,  although 
one  and  the  same  thing,  acts  like  two — viz.,  the  smooth  surface  is 
the  charged  body  X,  while  the  main  portion  of  the  shellac,  A,  acts 


3 8  FRICTIONAL    ELECTRICITY 

as  an  insulating  substance,  preventing  the  charge  on  X  from  neu- 
tralizing itself  with  the  metal  covering  D.  Therefore  when  the 
surface  of  the  shellac  is  rubbed  with  catskin,  we  have  the  follow- 
ing condition  in  A  :  the  surface  X  is  negatively  electrified,  and  by 
induction  the  metal  covering  D  is  positively  electrified,  because  it  is 


-> B 


FIG.  12. — THE  ELECTROPHORUS. 


connected  with  the  earth.  The  two  charges  are  separated  by  the 
insulated  shellac,  which  prevents  a  discharge,  and  thus  they  are 
held  in  their  relative  positions.  In  other  words,  the  minus  charge 
of  the  surface  X  influences  the  plus  charge  of  D,  and  conversely 


THE    ELECTROPHORUS 


39 


the  charge  on  D  tends  to  hold  the  charge  on  X.  Now,  when  we 
place  the  disk  B  on  X,  there  is  a  disturbance  of  the  electric  equilib- 
rium of  the  disk.  By  induction  its  under  surface  becomes  posi- 
tively electrified  and  its  upper  surface  becomes  negatively  electrified. 
By  touching  the  upper  surface  with  the  finger  we  connect  it  with 
the  ground,  and  thus  allow  the  disk  to  regain  its  equilibrium  in  its 
new  condition,  by  becoming  completely  and  positively  electrified. 
In  this  condition,  then,  we  have  the  negative  charge  on  X  firmly 
held  between  two  positive  charges — viz.,  that  on  the  disk  and  that 


FIG.  13. — HOLTZ  MACHINE. 


on  D  ;  and  this  shows  the  importance  of  grounding  D,  as  thus 
its  positive  charge  constantly  tends  to  hold  the  minus  charge  on  X. 
And  now  to  return  to  the  disk.  On  removing  it  from  the  shel- 
lac by  means  of  the  insulating  handle  it  retains  the  positive  charge 
it  has  acquired,  and  can  be  discharged  at  pleasure.  After  discharge 
the  process  can  be  repeated,  and  the  same  phenomena  will  take 
place  in  the  same  sequence. 


4O  FRICTIONAL    ELECTRICITY 

The  influence  machine  is  in  reality  a  form  of  revolving  elec- 
trophorus.  The  earliest  one  of  these  is  the  Holtz  machine  (Fig. 
13),  which  was  invented  in  1865.  This  machine  consists  of  two 
varnished  glass  disks,  one  a  little  larger  than  the  other,  and  placed 
three  millimeters  apart.  The  one  is  made  to  revolve,  and  the  other 
remains  stationary.  The  posterior  stationary  disk  is  insulated  and 
•contains  two  openings  cut  in  at  the  opposite  ends  of  any  diameter. 
Upon  the  edges  of  these  openings  are  pasted  tongues  of  cardboard 
coated  with  shellac,  the  tongues  pointing  in  the  same  direction  as 
the  axis  of  rotation  ;  so  that  if  one  is  directed  downward,  the  other 


FIG.  14. — DIAGRAM  SHOWING  THE  PRINCIPLE  OF  THE  HOLTZ  MACHINE. 

is  turned  toward  the  upper  part  of  the  disk.  These  are  called  arma- 
tures, and  serve  the  same  purpose  as  the  electrified  surface  in  the 
electrophorus.  In  front  of  the  anterior  rotating  plate,  and  opposite 
the  windows  of  the  stationary  one,  are  two  brass  combs,  connected 
respectively  with  a  horizontal  conductor  that  terminates  in  a  knob 
and  is  carried  by  an  insulating  support. 

In  order  to  set  the  machine  in  action,  the  knobs  of  the  conductors 
must  be  metallically  joined  ;  one  of  the  armatures  must  first  be 
electrified,  by  means  of  a  piece  of  hard  rubber,  for  instance,  that 
itself  has  been  previously  electrified  by  friction ;  and  the  rotary 


INDUCTION    MACHINES  4! 

plate  must  be  turned  in  a  direction  opposite  to  that  indicated  by 
the  points  of  the  armatures. 

The  working  is  complex,  but  by  reference  to  figure  14  its  prin- 
ciple will  be  made  clear. 

A  is  a  revolving  plate  placed  between  D,  a  piece  of  hard  rubber, 
corresponding  to  the  armatures  previously  described,  and  a  comb, 
B.  Let  the  potential  of  D  be  reduced  by  rubbing  it  with  catskin 
that  is  negatively  electrified.  By  induction  through  the  plate  the 
comb  B  will  become  positive  and  the  knob  N  negative.  But  the 
comb  readily  gives  up  its  plus  charge  to  the  glass,  so  that  the  sys- 
tem B  N  is  left  negatively  charged.  When  the  glass  disk  has 
made  half  a  revolution,  that  part  that  has  been  charged  positively 
from  the  comb  B  arrives  at  comb  B'.  Thus  the  two  conductors 
will  always  be  at  different  potentials,  and  a  steady  flow  of  sparks 
passes  between  P  and  N.  The  simplest  and  most  efficient  of  all 
induction  machines  is  the  Wimshurst  (Fig.  15).  It  consists  of 
two  circular  glass  plates  about  one  centimeter  apart,  mounted  on  a 
fixed  horizontal  spindle  in  such  a  way  that  they  will  rotate  in  oppo- 
site directions.  Both  disks  are  well  varnished,  and  attached  to  the 
outer  surface  of  each  are  narrow  radial  sections  of  tin-foil  and 
metal  buttons  placed  at  regular  intervals.  Attached  to  the  spindle 
on  which  the  disks  rotate  is  a  bent  conducting  rod  carrying  at  each 
of  its  ends  a  fine  wire  brush  ;  these  come  in  contact  with  the 
sections  of  foil  or  the  metal  buttons  when  the  plates  revolve.  At 
the  back  is  a  similar  bent  rod  placed  at  right  angles  to  the  one  in 
front.  Furthermore,  two  forks  are  provided  with  combs  directed 
toward  each  other  and  toward  the  plates  that  rotate  between  them. 
The  combs  are  supported  on  Leyden  jars,  to  which  are  also 
attached  the  dischargers.  The  machine  is  entirely  self-exciting  and 
requires  no  friction  or  charging  to  start  it.  The  initial  charge  is 
probably  obtained  from  the -atmospheric  electricity.  The  presence 
of  the  brushes,  buttons,  and  metal  inductors  is  somewhat  detri- 
mental to  the  insulation  of  this  machine,  so  that  the  energy  pro- 
duced is  less  than  that  given  by  a  Holtz  machine  of  the  same  size. 
The  Wimshurst  machine  is  especially  trustworthy  in  charging  and 
for  creating  a  difference  of  potential,  because  a  large  amount  of 
friction  is  developed  between  the  metallic  brushes  and  the  metallic 


42 


FRICTIONAL    ELECTRICITY 


sections  or  buttons  on  the  plate.  These  sections  or  buttons  are 
more  numerous  than  those  on  the  Toepler  machine,  and  this, 
together  with  the  fact  that  the  plates  are  made  to  rotate  in  opposite 
directions,  favors  the  rapid  development  of  a  charge. 

The  Toepler  machine  just  mentioned  is  simply  an  elaborated 
modification  of  the  Holtz. 


FIG.  15. — WIMSHURST  MACHINE. 

The  power  of  these  machines  may  be  materially  strengthened  by 
suspending  two  condensers  from  the  conductors. 

Materials  other  than  glass  have  been  used  for  the  plates  in  the 
static  machines,  and  various  claims  are  made  for  them.  Among 
these,  the  mica-plate  machine  maybe  mentioned;  in  this  the 
revolving  plates  are  made  of  mica,  while  the  stationary  plates  are  of 
glass.  It  is  claimed  for  these  machines  that  they  do  not  lose  their 


CONDENSERS  43 

charge  so  readily,  because  mica  does  not  collect  moisture,  and 
that  the  polarity  of  the  machine  remains  constant. 

The  condenser  is  an  apparatus  for  storing  up  a  large  amount 
of  electricity  upon  a  small  surface.  It  consists  in  all  cases  of  two 
insulated  conductors  separated  by  a  nonconductor,  and  acts  by 
induction.  A  simple  condenser  is  made  of  two  metal  plates  :  a 
lower  one  that  rests  with  its  under  surface  upon  an  insulating  glass 
foot  and  has  its  upper  surface  covered  with  a  thin  coating  of  insulat- 
ing shellac  ;  and  an  upper  plate  to  whose  upper  surface  an  insulating 
handle  is  attached  (Fig.  16).  If  the  upper  plate  is  now  placed  upon 
the  lower  one  and  the  latter  is  touched  by  a  positively  electrified 
body,  while  a  connection  is  established  between  the  upper  one  and 
the  earth,  the  lower  plate  will  take  a  certain  positive  charge. 
According  to  the  principles  already  explained, 
the  upper  plate  will  become  negative,  and,  by 
attracting  the  plus  potential  of  the  lower  plate, 
will  not  allow  this  to  become  free,  but  keeps  it 
fixed — /.  e.,  free  from  tension.  As  a  result  of 
this  the  lower  plate  will  be  able  to  absorb  more 

electricity   from   its   source,  and   this   again  will 

'  FIG.    16. — METAL 

cause  a  further  accumulation  of  negative  elec-      PLATE  CONDENSER. 
tricity  on  the  upper  plate.     Thus  it  will  be  seen 
that  the  capacity  of  the  lower  plate  will  be  increased,  and  that  of 
the  upper  plate  will  also  be  correspondingly  enlarged,  but  will,  of 
course,  possess  the  opposite  potential.     If  the  connection  between 
the  upper  plate  and  the  earth  be  broken  and  this  plate  be  lifted  by 
its  insulating  handle  from  the  lower  one,  the  electricity  contained 
in  the  latter  will  no  longer  be  held  down,  but  will  become  free  and 
may  be  discharged  at  will.     Condensers  of  modified  form  are  shown 
in  figures  17  and  18. 

Upon  the  same  principle  as  the  condenser  is  based  the  Franklin 
plate. 

The  Franklin  plate,  or  fulminating  pane,  consists  of  a  glass 
plate  partially  covered  on  both  sides  by  tin-foil  ;  a  broad  border  on 
both  sides  of  the  plate  remains  free  from  foil  and  is  varnished  with 
shellac.  The  anterior  surface  of  the  plate  (corresponding  to  the 
lower  surface  of  the  condenser)  is  connected  with  the  conductor  of 


44 


FRICTIONAL    ELECTRICITY 


an  electric  machine ;  the  posterior  surface  (corresponding  to  the 
upper  or  collector  plate  of  the  condenser)  is  placed  in  connection 
with  the  earth.  The  charging  of  the  two  surfaces  is  carried  out  in 


FIG.  17. — CONDENSER. 


FIG.  1 8. — CONDENSER. 


the  manner  described  for  charging  the  condenser.  Such  a  ful- 
minating pane,  rolled  up,  constitutes  a  Leyden  or  Kleist  jar 
(Fig.  19). 

The  Leyden  jar  is  most  conveniently  made  of  a  glass  bottle  of 
suitable  size,  coated  on  its  inner  and  outer  sur- 
faces for  about  two-thirds  of  its  height  with  tin- 
foil.    The  uncovered  surface  is   coated  with  an 
insulating  varnish  ;    the  mouth  of  the  bottle  is 
closed  by  an  insulated  cork  ;  through  this  cork 
passes  a  metal  rod,  ending  externally  in  a  knob 
and  internally  being  in  communication  with  the 
tin-foil.     When,   now,   the  metal    knob  is  con- 
nected with  the  conductor  of  an  electric  machine 
and  the  outer  covering  of  tin-foil  is  connected 
with  the  earth,  this  apparatus  may  be  charged 
in  the  same  manner  as  the  two  preceding  ones. 
It  is  discharged  explosively  by  forming  a  connection  be- 
tween the  two  coverings.      It  may  thus  safely  be  grasped  by  either 
alone,  but  if  carelessly  handled,  may  give  the  operator  a  severe 
shock.     All  actions  of  the  electric  machines  may,  by  means  of 
such  bottles,  be  materially  increased. 


FIG.   19. — LEYDEN 
OR  KLEIST  JAR. 


CHAPTER  III 
DYNAMIC   ELECTRICITY 

Chemical  Generators.  Galvanism.  Voltaic  Pile.  Current.  Circuit. 
Cells.  Elements.  Electrolyte.  Various  Forms  of  Cells.  Battery. 
Positive  and  Negative  Plates.  Poles.  Current  Direction.  Pressure. 
Resistance.  Ohm' s  Law.  Arrangement  of  Cells. 

Electricity  in  equilibrium,  which  we  have  just  studied,  is  known 
as  static  electricity ;  electricity  in  motion  is  known  as  dynamic 
electricity.  Any  two  substances  placed  in  contact,  or  in  a  liquid, 
will  show  a  difference  in  potential ;  but  only  a  few,  especially  the 
metals  and  carbon,  will  show  enough  difference  to  be  appreciable  by 
indicating  instruments. 

Even  the  greatest  differences  of  potential  thus  obtained  are  smaller 
than  those  produced  by  friction,  and  the  pith-ball  apparatus  would 
not  be  affected  by  them.  By  more  delicate  instruments  these  dif- 
ferences can  be  recognized.  Such  an  electrometer  of  most  sensitive 
character  is  called  Thompson's  quadrant  electrometer,  and  consists 
of  a  light  rod  or  needle  of  metal,  suspended  horizontally  by  a  fine 
wire  over  four  pieces  of  brass  forming  the  four  quadrants  of  a  circle. 
The  opposite  quadrants  are  connected  by  wires,  and  the  adjacent 
ones  are  insulated  from  each  other.  All  four  are  insulated  from 
the  rest  of  the  instrument,  and  the  whole  is  covered  by  a  glass 
shade.  The  suspended  rod  is  kept  at  a  high  positive  potential  by 
an  arrangement  the  principle  of  which  it  is  not  necessary  to  enter 
upon  here.  A  small  mirror  that  reflects  upon  a  screen  a  ray  of 
light  from  a  lamp  is  attached  to  the  rod  ;  hereby  the  smallest  move- 
ment of  the  needle  becomes  visible  upon  the  screen.  By  means  of 
such  an  instrument  we  can  observe  that  differences  of  potential  are 
manifested  upon  mere  contact  of  heterogeneous  substances.  It  was 
to  such  contact  alone  that  Volta  assumed  the  phenomena  produced 
by  the  pile  that  bears  his  name  to  be  due.  It  will,  however,  be  seen 
that  the  current  of  the  voltaic  pile  is  probably  due  to  chemical 

45 


46 


DYNAMIC    ELECTRICITY 


action.  This  pile  is  formed  by  the  superposition  of  a  certain  number 
of  couples.  Each  couple  is  composed  of  a  disk  of  copper,  C,  and  a 
disk  of  zinc,  Z,  separated  by  a  disk  of  cloth  that  is  saturated  with 
acidulated  water  (Fig.  20).  Each  one  of  these  couples  may  be  sur- 
rounded by  glass,  the  quantity  of  fluid  increased,  and  we  have  a 
galvanic  or  voltaic  cell.  Thus  a  cell  will  be  constituted 


FIG.  20. —VOLTAIC  PILE. 


essentially  by  an  isolating  jar  containing  a  fluid,  in  which  two  plates 
of  different  metal  are  immersed.  The  contact  or  chemical  action 
that  here  occurs  produces  a  difference  of  potential,  which  sets  in 
motion  an  electromotive  force.  Every  cell  is  characterized  abso- 
lutely by  the  electromotive  force  that  it  possesses,  and  by  the  con- 
ductivity, or  conversely  the  resistance,  that  it  presents  to  this  force. 


THE    GALVANIC    CURRENT  4/ 

If  the  free  ends  of  the  two  metals  that  are  immersed  in  the  fluid  are 
connected  by  a  conductor  of  electricity, — for  instance,  a  copper  wire, 
— the  various  potentials  begin  to  equalize  themselves  in  the  closed 
circuit,  consisting  of  metal  i,  fluid,  metal  2,  and  copper  wire,  as 
shown  in  figure  21  ;  and  inasmuch  as  the  constant  contact  of  the 
metals  with  the  fluid  produces  an  accumulation  of  electric  energy 
that  is  constantly  being  renewed,  the  equalization  of  potentials  will 
not  only  be  momentary,  but  will  be  kept  up  constantly.  This 
equalization  of  potentials  in  the  connecting  wire  we  call  the  elec- 
tric current,  and  the  all-round  path  is  called  a  circuit. 

We  have  already  spoken  of  current  in  the  chapter  on  Frictional 
Electricity,  but  there  we  were  always  dealing  with  momentary 
currents.  No  matter  how  rapidly  spark  follows  upon  spark  or  dis- 
charge follows  upon  discharge,  there  is  always  an  appreciable  gap 
between  them,  due  to  a  pause  in  the  collection 
of  electricity  from  its  source.  In  contradistinc- 
tion thereto,  the  current  that  is  produced  by 
the  voltaic  cell  is  a  constant  one,  and  the  cur- 
rent derived  from  such  a  cell  is  also  known  as 
the  constant  or  galvanic  current.  The 

latter    name    has    been    generally   adopted   by 

&  J  FIG.    21. — SIMPLEST 

medical  writers  in  honor  of  Galvani.  FORM  OF  CELL. 

All  voltaic    cells    may  be    divided   into    two 

general  classes:  (i)  The  single -fluid  cells,  or  those  that  have 
but  one  exciting  fluid.  (2)  The  double- fluid  cells,  or  those 
that  have  two  exciting  fluids. 

Every  voltaic  cell  consists  of  two  essential  parts  :  (i)  A  voltaic 
pair,  or  voltaic  couple.  (2)  One  or  two  exciting  fluids. 

The  two  substances  forming  the  voltaic  couple  are  called  the 
elements;  the  fluid  is  called  the  electrolyte  of  a  cell.  The 
elements,  which  generally  consist  of  two  dissimilar  metals,  although 
they  may  be  formed  of  a  variety  of  substances,  are  known  as  the 
positive  and  negative  plates,  the  positive  plate  always  being 
the  one  that  is  most  attacked  or  acted  upon  by  the  electrolyte.  If 
such  a  couple,  say  one  of  copper  and  zinc,  be  immersed  in  dilute 
sulphuric  acid,  so  far  as  can  be  seen  no  change  takes  place, 
although  the  maximum  electromotive  force  of  the  couple  must  be 


48  DYNAMIC    ELECTRICITY 

set  up.  As  soon,  however,  as  the  plates  are  joined  externally  by 
a  conductor,  bubbles  of  hydrogen  will  be  seen  to  form  at  the 
copper  plate. 

The.se  bubbles  set  up  a  counter  electromotive  force,  known  as 
polarization,  and  also  reduce  the  conductivity  of  the  cells — that 
is  to  say,  increase  the  internal  resistance.  As  a  result  of  both 
of  these  processes  the  capability  of  the  cell  to  furnish  current  is 
diminished. 

The  bad  effects  of  polarization  may  be  overcome  in  a  variety  of 
ways  : 

1.  Mechanically,  by  loosening  the  bubbles  from  the  plate  to 
which  they  adhere — that  is,  by  brushing  them  away  or  by  agi- 
tating the  liquid. 

2.  Chemically,  by  surrounding  the  plate  upon  which  the  bubbles 
of  hydrogen  form,  by  some  powerful  oxidant,  one  that  will  oxidize 
the  hydrogen  without  having  an  injurious  effect  upon  the  cell ;  or 
by  making  use  of  the  hydrogen  for  some  chemical  decomposition, 
which,  however,  must  also  be  innocuous  to  the  cell  itself. 

The  first  method  is  rather  impracticable,  and  therefore  it  is  the 
second  method  that  is  satisfactorily  made  use  of  in  various  kinds  of 
cells. 

As  the  voltaic  cell  is  an  important  source  of  electromotive  force 
as  employed  in  therapeutics,  we  shall  briefly  describe  some  of  the 
most  practical  forms. 

Cells. — One  of  the  first  successful  attempts  at  modifying  the 
evils  of  polarization  was  made  in  1836  by  Professor  Daniell. 

The  Daniell  cell  (Fig.  22)  consists  of  an  outer  glass  jar,  G, 
containing  a  split  cylinder  of  zinc,  z,  inside  of  which  is  a  porous 
jar,  P,  of  unglazed  earthenware,  and  inside  of  this  a  copper 
cylinder,  c,  at  the  top  of  which  is  a  perforated  ledge,  upon  which 
are  placed  crystals  of  cupric  sulphate,  or  blue  stone.  The  outer 
zinc  cylinder  is  immersed  in  dilute  sulphuric  acid  ;  the  inner  copper 
cylinder,  in  a  solution  of  cupric  sulphate.  The  crystals  of  cupric 
sulphate  upon  the  ledge  of  the  cylinder  keep  the  solution  in  a  state 
of  saturation. 

As  soon  as  the  cell  is  placed  in  action,  the  zinc  and  copper 
plates  being  joined  externally  by  a  conductor,  the  zinc  is  attacked 


VOLTAIC    CELLS  49 

by  the  sulphuric  acid,  the  hydrogen  of  the  latter  is  set  free,  and 
zinc  sulphate  is  formed.  The  freed  hydrogen  passes  through  the 
porous  jar  and  comes  into  contact  with  the  copper  sulphate  ;  here 
it  takes  the  place  of  the  copper,  leaving  this  free  and  forming  sul- 
phuric acid.  The  freed  copper  from  the  copper  sulphate  solution 
becomes  fixed  upon  the  copper  plate,  thus  always  giving  a  clean 
copper  surface. 

Thus  the  copper  sulphate  is  employed  to  take  up  the  objection- 
able hydrogen,  and  a  cell  is  thereby  obtained  with  little  or  no 
polarization.  Its  electromotive  force,  however,  is  small,  and  its 
internal  resistance  is  large. 

This  Daniell  cell  has  been  variously  modified  in  order  to  effect  a 


CUEEN-C0.9HILA. 

FIG.  22. — DANIELL  CELL. 

diminution  of  the  internal  resistance ;  thus  the  porous  jar  has  been 
eliminated,  and  solutions  of  different  density — copper  sulphate  and 
zinc  sulphate — surround  the  horizontally  placed  elements  of  the 
cell ;  as  the  specific  gravity  of  the  copper  sulphate  solution  is 
greater  than  that  of  the  zinc  sulphate,  the  former  is  placed  at  the 
bottom  of  the  vessel,  while  upon  it,  but  of  course  not  mixing  with 
it,  is  poured  the  solution  of  zinc  sulphate. 

Such  cells  are  also  often  called  gravity  cells  (Figs.  23  and 

24). 

Grove    Cell. — In  the  cell  invented  by  Grove  and  known  by 
his  name  the  hydrogen  is  gotten  rid  of,  and  at  the  same  time  a 
higher  electromotive  force  is  obtained,  by  surrounding  the  copper 
4 


DYNAMIC    ELECTRICITY 


element,  or  its  substitute,  with  a  strong  oxidizing  agent  In  the 
Grove  cell  the  copper  of  the  Daniell  cell  is  replaced  by  platinum, 
and  the  copper  sulphate  by  nitric  acid. 

Thus  this  cell  consists  of  zinc  in  dilute  sulphuric  acid  outside  of 


FIG.  23. — GRAVITY  CELL. 


FIG.  24. — GRAVITY  CELL. 


the  porous  jar,  and  platinum  in  nitric  acid  inside  the  porous  jar. 
When  the  cell  is  in  action,  the  zinc  is  attacked  and  zinc  sulphate 
formed,  as  in  the  Daniell  cell ;  the  free  hydrogen  coming  into  con- 
tact with  the  nitric  acid  takes  oxygen  from  it  and  forms  water, 


Hflr  ~ffl 
FIG.  25. — GROVE  CELL. 

leaving,  however,  another  compound  of  nitrogen  and  oxygen,  which 
is  given  off  in  poisonous  red  fumes,  so  that  this  battery  cannot  be 
utilized  unless  some  means  is  employed  for  carrying  off  these 
fumes.  Although  polarization  is  effectually  prevented  in  this  cell, 


SINGLE-FLUID    CELLS  51 

the  nitric  acid  soon  becomes  very  weak  and  the  sulphuric  acid  is 
soon  replaced  by  zinc  sulphate.  The  electromotive  force,  which  in 
the  beginning  is  large,  rapidly  decreases.  The  Grove  cell  is  shown 
in  figure  25. 

Bunsen  Cell. — On  account  of  the  high  cost  of  platinum, 
Bunsen  suggested  the  use  of  hard  gas-coke  or  carbon  as  a  substi- 
tute, and  this  modification  is  known  as  the  Bunsen  cell  (Fig.  26). 

While  the  electromotive  force  of  the  Bunsen  cell  is  about  the 
same  as  that  of  the  Grove,  its  internal  resistance  is  higher,  but  its 
current  lasts  longer. 


FIG.  26. — BUNSEN  CELL  AND  ITS  COMPONENT  PARTS. 


Single-fluid  Cells. 

For  simplicity  in  construction,  cells  employing  a  single  exciting 
fluid,  simple  or  compound,  have  been  devised. 

Zinc-platinum  Cell. — This  cell,  known  as  Smee's,  consists 
of  a  plate  of  zinc  and  a  plate  of  platinized  silver,  dipping  in  dilute 
sulphuric  acid.  The  electromotive  force  is  low. 

Zinc -carbon  Cell. — This  consists  of  a  pair  of  zinc  and  car- 
bon plates,  dipping  into  a  weak  solution  of  sulphuric  acid  (i  :  10  or 
20  of  water).  The  electromotive  force  is  somewhat  higher  than 
that  of  Smee's  cell. 

Bichromate  or  Chromic  Acid  Cell s. — In  order  to  do  away 
with  the  objectionable  fumes  arising  from  the  use  of  nitric  acid  as 
an  oxidant,  chromic  acid  and  potassium  bichromate  have 
been  largely  used  in  substitution.  There  are  many  forms  of  these 
cells. 


DYNAMIC    ELECTRICITY 


Grenet  Cell. — Such  a  cell,  one  largely  used  for  medical  pur- 
poses, is  the  Grenet.  This  consists  of  a  glass  flask,  into  which 
reach,  from  a  cover  of  hard  rubber,  two  carbon  plates  and  an  adjust- 
able zinc  plate  attached  to  a  long  brass  rod  (Fig.  27). 

The  carbon  plates  reach  to  the  bottom  of  the  vessel,  while  the 
zinc  plate  may  be  pressed  down  into  the  lower  half  of  the  vessel 
that  contains  the  fluid,  or  may  be  drawn  to  the  upper  part,  so  that 
it  does  not  come  in  contact  with  the  fluid  at  all.  By  this  means  the 
cell  is  easily  put  into  and  out  of  action. 

Amalgamation. — In  all  zinc-carbon  cells  the  zinc  is  chemically 
attacked  by  the  acid  of  the  electrolyte.  When  impure  zinc  is  used, 


FIG.  27. — GRENET  CELL. 

as  is  usually  the  case  on  account  of  the  difficulty  of  obtaining  pure 
zinc  (the  ordinary  zinc  of  commerce  contains  more  or  less  iron  or 
lead,  and  these  metals  are  electronegative  to  zinc),  a  series  of 
elements  is  formed  between  the  impurities  of  the  zinc  and  the  zinc 
itself.  These  minute  couples  of  elements  when  attacked  by  the  elec- 
trolyte form  complete  circuits.  The  action  of  these  couples  is  called 
local  action,  and  the  electric  energy  thus  generated  cannot  be 
utilized.  It  has  been  found  that  such  local  action  can  be  avoided 
by  rubbing  the  clean  zinc  plate  with  mercury.  When  mercury  is 
rubbed  over  the  plate,  it  dissolves  the  zinc  and  forms  a  coating  of 
zinc  amalgam  on  the  plate.  The  impurities  are  not  dissolved,  so 


LECLANCHE    CELL  53 

that  it  is  only  the  zinc  amalgam  that  comes  in  contact  with  the  acid. 
As  fast  as  the  zinc  of  the  amalgam  is  acted  upon  by  the  acid,  just 
so  fast  does  the  mercury  dissolve  fresh  zinc  from  the  plate. 

The  electromotive  force  of  this  cell  is  high,  but  its  constancy  is 
not  great. 

A  good  solution  for  such  a  cell  is  as  follows  : 

Grams. 

Potassium  bichromate, 15 

Sulphuric  acid, 15 

Water, 250 

Mercury  oxysulphate, 5 

The  use  of  the  mercury  oxysulphate  is  for  the  amalgamation  of 
the  zinc. 

Instead  of  the  foregoing  fluid,  electropoion  fluid  may  be 
used.  This  is  made  by  adding  two  parts  of  sulphuric  acid  to  eight 
parts  of  water,  and  while  the  mixture  is  still  hot  stirring  in  one  part, 
by  weight,  of  pulverized  potassium  bichromate.  As  soon  as  it  is 
cold  it  is  ready  for  use.  An  earthen  vessel  should  be  used  for 
mixing.  When  this  fluid  is  used,  the  zinc  must  be  amalgamated 
more  frequently.  This  may  be  done  in  the  following  way  :  Mix  250 
grams  of  nitric  acid  with  500  grams  of  hydrochloric  acid,  and  then 
slowly  add  125  grams  of  mercury ;  when  dissolved,  add  700  grams 
more  of  hydrochloric  acid,  and  stir  well.  Cleanse  the  zinc  with 
potash,  and  dip  it  into  the  foregoing  solution  for  several  seconds. 
Rinse  in  clear  water  and  rub  with  a  stiff  brush.  The  amalgama- 
tion may  be  effected  in  a  simpler  manner  by  first  dipping  the  zincs 
into  dilute  sulphuric  acid  to  cleanse  them,  then  dipping  them  into  a 
vessel  of  mercury,  and  finally  allowing  the  surplus  to  drain  off. 

Leclanche  Cell. — The  Leclanche  cell  is  a  zinc-carbon  couple 
with  an  electrolyte  of  ammonium  chlorid  (sal  ammoniac),  and 
with  manganese  peroxid  as  a  depolarizer.  The  action  de- 
pends on  the  ammonium  chlorid  giving  up  free  ammonia  and 
forming  zinc  chlorid.  Other  chemical  actions  also  take  place. 
Finally  hydrogen  is  liberated,  which  comes  in  contact  with  the 
manganese  peroxid  and  reduces  it  to  a  lower  oxid. 

Manganese  peroxid  parts  with  its  oxygen  comparatively  slowly, 
so  that  if  hydrogen  is  produced  too  rapidly, — and  this  is  the  case 


54 


DYNAMIC    ELECTRICITY 


when  the  cell  is  working, — only  a  part  of  it  is  neutralized.  If, 
however,  the  cell  is  used  only  for  a  short  time  and  then  allowed  to 
rest,  the  hydrogen  is  gradually  neutralized 
and  the  cell  soon  recovers  its  normal  state. 
These  cells  are  admirably  adapted  for 
medical  work,  require  very  little  attention, 
last  for  a  long  time  when  properly  used, 
and  are  easily  renewed. 

In  the  original  form  this  cell  con- 
tained a  porous  jar  filled  with  the  de- 
polarizing material,  in  the  center  of  which 
was  placed  the  carbon  plate  (Fig.  28). 
As  the  sole  office  of  the  porous  jar  was 
to  keep  the  material  together,  Leclanche 
abandoned  it,  and  accomplished  its  pur- 
pose by  compressing  a  mixture  of  carbon, 
manganese  peroxid,  gum,  and  a  small 

quantity  of  potassium  bisulphate  into  a  hard  mass,  after  keeping 
the  mixture  for  some  time  at  the  temperature  of  boiling  water. 
Plates  of  this  compressed  material  are  fastened,  one  at  each  side 


FIG.    28.  —  ORIGINAL 
LECLANCHE  CELL. 


FIG.  29. — LECLANCHE  CELL  WITHOUT  POROUS 
CUP. 


FIG.  30. — MODIFIED  LECLANCHE 
CELL. 


of  the  carbon  element,  by  means  of  rubber  bands.  The  internal 
resistance  of  these  cells  is  lower  than  that  of  those  containing  the 
porous  cups  (Fig.  29). 


SILVER    AND    DRY    CELLS 


55 


A  practical  modification  of  this  form  of  cell  is  shown  in  fig- 
ure 30. 

Here  the  depolarizing  mixture  is  contained  in  two  bags,  which  are 
tied  on  the  opposite  sides  of  the  carbon  elements,  thus  allowing  free 
circulation  of  the  solution. 

Another  very  practical  modification  of  the  Leclanche  cell  is  the 
Law  telephone  cell,  shown  in  figure  31. 

The  silver  chlorid  cell  consists  of  a  zinc-silver  couple,  im- 
mersed in  a  dilute  aqueous  solution  of  sal  ammoniac  and  sodium 
chlorid.  As  made  by  Gaiffe,  it  consists  of  a  plate  of  zinc,  Z  (Fig. 
32),  and  a  plate  of  silver  chlorid,  Y,  fused  around  a  wire  and  envel- 


FIG.  31. — LAW  TELEPHONE  CELL. 


FIG.  32. — SILVER  CHLORID  CELL. 


oped  in  a  cotton  bag,  the  whole  contained  in  a  vessel  of  hard  rub- 
ber hermetically  sealed  by  a  cork,  to  the  top  of  which  are  attached 
the  binding  posts  for  making  connections.  A  cushion  composed 
of  six  or  eight  sheets  of  blotting-paper  fills  the  space  between  the 
two  elements,  keeps  them  apart,  and  is  saturated  with  the  exciting 
fluid. 

Dry  cells,  so  called,  are  not  really  dry,  and  their  name  is  badly 
chosen,  since  their  action  is  dependent  upon  the  presence  of  a  liquid 
electrolyte.  The  liquid  used  is,  however,  made  into  a  paste  with 
some  gelatinous  substance  or  powdered  material ;  in  so  far  as  they 
contain  no  free  liquid,  they  may  be  considered  dry. 


56  DYNAMIC    ELECTRICITY 

Batteries. 

When,  now,  we  properly  connect  a  number  of  cells,  of  whatsoever 
construction,  we  have  a  battery.  The  chemical  action  upon  one 
of  the  plates  of  the  cell  must  be  greater  than  upon  the  other  in  order 
to  produce  a  difference  of  potential,  and  the  plate  that  is  most  at- 
tacked is  called  the  active  orpositiveplate;  the  other  is  the  inert 
or  negative  plate.  As  electricity  always  flows  from  a  point  of 
higher  potential  toward  one  of  lower  potential,  the  direction  in  the 
liquid  will  be  from  the  plate  most  attacked — e.  g.,  in  a  zinc-carbon  cell, 


1 

! 

\ 

\~f 

c-~-  -  -z 

- 

- 

; 

1 

- 

—mm 

»  —      .  —    -    , 

*~  ! 

FIG.  33. — SHOWING  THE  FLOW  OF  CURRENT  FROM  POSITIVE  TO  NEGATIVE  PLATE, 
AND  FROM  POSITIVE  TO  NEGATIVE  POLE. 

from  the  zinc  to  the  carbon — from  the  positive  to  the  negative  plate. 
If  to  each  plate  or  element  a  conducting  wire  be  attached,  the  current 
will  spread  through  each  such  wire,  and  inasmuch  as  the  higher  poten- 
tial of  the  zinc  forces  the  current  to  the  carbon,  and  through  the  car- 
bon into  the  conducting  wire,  the  wire  attached  to  the  carbon  will  be 
found  to  be  of  higher  potential  than  is  that  attached  to  the  zinc.  The 
terminal  of  the  plate  that  is  out  of  the  fluid,  or  the  end  of  the  con- 
ductor attached  to  this  terminal,  is  called  the  pole  or  electrode. 


ELECTROMOTIVE    SERIES    AND    PRESSURE  57 

It  will  thus  be  apparent  that  the  negative  plate  of  the  cell  will 
carry  the  positive  pole;  and  that  therefore  outside  of  the  cell  the 
current  flowing  from  the  positive  to  the  negative  pole  will  flow  from 
the  negative  to  the  positive  plate.  Whatever  misunderstanding  may 
arise  in  regard  to  this  must  be  due  to  the  fact  that  the  terms  plate 
and  pole  are  not  clearly  differentiated.  The  accompanying  illus- 
tration (Fig.  33)  will  render  this  clear. 

We  should  always  remember  that  in  speaking  of  current  we  refer 
to  a  flow  from  a  higher  to  a  lower  level.  Any  substance  that  is 
of  a  higher  potential  than  another  with  which  it  is  placed  in 
connection,  by  whatsoever  medium,  will  be  electropositive, 
while  the  other  would  be  electronegative.  Such  a  list  of 
substances,  placing  the  bodies  of  higher  potential  first,  is  called 
an  electromotive  series.  Of  course,  the  current  in  the  wire 
externally  connected  will  proceed  from  the  body  lower  in  the  list 
to  a  higher  one.  Such  a  list  is  the  following  : 

Zinc  Nickel  Copper 

Cadmium  Bismuth  Silver 

Tin  Antimony  Gold 

Lead  Platinum 

Iron  Graphite. 

From  this  it  will  be  seen  that  if  the  elements  of  a  cell  are  consti- 
tuted of  zinc  and  copper,  the  current  in  the  wire  will  flow  from 
the  copper  to  the  zinc,  while  in  a  copper-graphite  combination  the 
flow  will  be  from  the  graphite  to  the  copper. 

Pressure. 

In  order  to  gain  a  clearer  insight  into  electromotive  force  and 
the  laws  that  govern  it,  let  us  call  it  pressure,  and  compare  it 
with  the  pressure  of  water. 

Let  us  take  a  glass  jar  filled  with  water  and  connected  to  a  glass 
tube  by  means  of  a  piece  of  rubber  tubing,  and  place  the  entire 
apparatus  on  a  table.  If  we  lift  the  jar  of  water  from  the  table,  the 
glass  tube  remaining  stationary,  the  water-level  in  the  glass  tube 
will  at  once  rise  until  it  has  attained  the  level  of  the  water  in  the 
jar.  The  higher  we  raise  the  jar,  the  higher  will  rise  the  water  in 
the  tube  (Fig.  34).  Thus  the  pressure  of  the  water  is  proportional 


DYNAMIC    ELECTRICITY 


to  the  difference  of  level  ;  increasing  this  difference  increases  the 
pressure  ;  decreasing  it  decreases  the  pressure. 

The  difference  of  electric  potential  is  the  cause  of  electric  pressure, 
and  here  also  the  pressure  is  proportional  to  the  difference  of  poten- 
tial, and  by  increasing  or  decreasing  the  latter  we  increase  or 
decrease  the  former. 

Resistance. — The  opposition  that  the  path  of  a  current  furnishes 
to  its  flow  can  best  be  understood  by  like  comparison  with  the  flow 
of  water.  Thus,  if  in  a  cistern  of  water  the  pressure  be  kept  con- 
stant by  a  continuous  inflow,  and  water  be  allowed  to  escape  from  a 


LEVEL         B 


C7. 


LEVEL         A 


// 


/.EVEL          A 


FIG.  34. — SHOWING  VARIATIONS  IN  WATER  PRESSURE. 

pipe  of  a  certain  area  at  the  bottom  of  the  cistern,  then  a  certain 
quantity  of  water  will  escape  in  a  given  time.  If  the  area  of  this 
escape  pipe  be  made  smaller,  the  water  of  the  outflow  will  be  cor- 
respondingly diminished.  If  the  area  of  such  a  pipe  be  doubled, 
or,  what  is  the  same,  if  two  such  escape  pipes  be  furnished,  the  rate 
of  the  outflow  will  also  be  doubled.  The  rate  of  flow  can  also  be 
increased  or  diminished  by  largely  increasing  or  decreasing  the 
length  of  the  pipe,  for  its  walls  offer  some  resistance  to  the  flow 
of  water,  and  thus  an  increase  in  length  would  increase  the  resis- 
tance, and  through  this  oppose  the  flow,  while  the  decrease  would 


CONDUCTION    AND    RESISTANCE  59 

diminish  the  resistance  and  facilitate  the  flow.  Therefore  the  flow 
of  water  under  constant  pressure  would  be  directly  proportional  to 
the  area  or  caliber  ol  the  pipe,  while  it  is  inversely  proportional  to 
the  length  of  the  pipe.  These  principles  govern  the  flow  of  elec- 
tricity also. 

As  already  stated,  electric  conduction  is  the  reverse  of  resistance, 
so  that  a  good  conductor  offers  slight  resistance  to  the  flow  of  the 
current.  The  metals,  being  good  conductors  of  electricity,  offer 
least  resistance  to  its  flow.  The  following  table  of  conductors 
may  therefore  be  used  in  inverse  order  as  a  table  of  resistances, 
the  good  conductors  being  bodies  of  slight  resistance,  the 
semiconductors  being  bodies  of  great  resistance,  and  the 
insulators  being  bodies  of  so  great  resistance  that  they  almost 
effectually  oppose  the  passage  of  any  current. 

TABLE  OF  CONDUCTORS  AND  RESISTANCES. 

GOOD  CONDUCTORS.  SEMICONDUCTORS.  INSULATORS. 

Silver.  Carbon.  Wool. 

Copper.  Graphite.  Silk. 

Gold.  Acids.  Sealing-wax. 

Aluminum.  Saline  solutions.  Sulphur. 

Zinc.  Sea-water.  Resin. 

Platinum.  Melting  ice.  Gutta-percha. 

Iron.  Pure  water.  India-rubber. 

Tin.  Stone.  Shellac. 

Lead.  Dry  ice.  Paraffin. 

German  silver.  Dry  wood.  Vulcanite. 

Antimony.  Porcelain.  Glass. 

Mercury.  Dry  paper.  Dry  air. 

(Slight  Resistance.)  (High  Resistance.)  (Very  High  Resistance.) 

Usually  copper  wire  is  employed  for  electric  conductors. 

If  we  examine  the  circuit  of  an  electric  current,  we  see  that  it, 
consists  of  a  cell  and  of  the  connecting  wire,  so  that  the  resistance 
of  the  entire  circuit  will  include  the  resistance  of  the  metals  and 
the  liquid  of  the  cell  and  of  the  wire,  as  well  as  of  every  other 
conductor  that  may  join  the  poles  of  the  cell.  The  resistance  of 
the  cell  itself  is  called  the  internal  resistance  of  the  circuit; 
that  of  the  other  parts,  the  external  resistance.  The  former 
is  symbolized  by  "  r,"  the  latter  by  "  R." 


6o 


DYNAMIC    ELECTRICITY 


The  Electric  Circuit. — If,  now,  instead  of  the  cistern  of  water 
we  make  use  of  an  electric  apparatus  for  the  production  of  pres- 
sure, and  connect  one  side  of  the  apparatus  with  the  other  so  as  to 
establish  a  continuous  path,  we  shall  find  that  the  same  laws  apply, 
and  we  shall  learn  more  regarding  the  laws  that  govern  the  flow  in 
a  circuit.  In  order  to  have  some  indication  of  the  flow  of  current, 
we  place  in  the  external  circuit  a  galvanometer.  The  galvan- 
ometer is  an  instrument  that,  by  the  deflection  of  its  needle,  shows 
the  strength  of  an  electric  current  passing  through  it  ;  the  principle 
and  construction  of  such  an  instrument  will  be  discussed  later. 

Thus,  in  figure  3  5  the  external  circuit  is  made  up  of  three  wires, 


FIG.  35. — SHOWING  A  SIMPLE  CIRCUIT  CONTAINING  THREE  EQUAL  RESISTANCE 

WIRES. 


each  being  of  the  same  length  and  caliber,  thus  giving  the  same  oppo- 
sition to  the  flow  of  current.  Into  the  circuit  is  also  introduced  a 
galvanometer,  G.  The  needle  of  the  galvanometer  swings  to  a 
certain  point.  If  one  of  the  wires  be  removed,  the  needle  comes 
back  to  the  point  of  rest  that  it  occupied  before  its  introduction  into 
the  circuit,  thus  showing  that  no  current  flows  unless  the  path  is 
continuous.  If  the  wire  I,  2,  or  3,  be  removed  and  replaced  by 
another  of  equal  length  but  of  larger  cross-section,  the  needle  will 
be  deflected  to  a  greater  extent  than  in  the  first  experiment,  showing 
that  more  current  passes  in  consequence  of  the  increased  diam- 
eter of  the  new  wire,  and  that  it  does  not  matter  where  the  circuit 


ALTERATION    OF    RESISTANCE 


61 


is  altered,  the  deflection  always  being  the  same.  If  two  wires  be 
replaced  by  thicker  ones,  the  needle  will  be  still  further  deflected, 
and  still  more  so  if  all  three  wires  be  changed.  Such  a  circuit, 
made  up  of  one  continuous  path,  is  said  to  be  a  simple  circuit ; 


B 


FIG.  36. — SHOWING  A  SIMPLE  CIRCUIT  CONTAINING  ONE  RESISTANCE  WIRE. 

when  the  circuit  consists  of  two  or  more  branches,  it  is  said  to  be 
a  divided  circuit. 

If  we  make  a  circuit  with  one  resistance  coil  interposed  and  note 
the  deflection  of  the  galvanometer  needle  (Fig.  36),  and  then  join 
to  this  resistance  coil  another  of  the  same  length  and  thickness  of 
wire  (Fig.  37),  the  resistance  having  been  doubled,  the  deflection 


FIG.  37. — SHOWING  A   SIMPLE  CIRCUIT  CONTAINING  Two  RESISTANCE  WIRES  IN 

SERIES. 

will  be  one-half  of  what  it  was  before  ;  but  if,  instead  of  joining 
the  wires  end  to  end  or  in  series  we  place  them  side  by  side,  as  in 
figure  38,  the  deflection  will  be  doubled,  for  here  we  have,  by  put- 
ting the  wires  side  by  side  in  parallel,  doubled  the  thickness  with- 
out changing  the  length. 


62 


DYNAMIC    ELECTRICITY 


Thus,  increasing  the  length  of  the  wire  increases  its  resistance, 
and  increasing  its  thickness  decreases  its  resistance,  as  we  shall  show 
later.  Inasmuch  as  the  deflection  of  the  galvanometer  needle  is  pro- 
portional to  the  current  that  influences  it,  we  may  say  that  current 
varies  inversely  as  resistance. 

If,  furthermore,  in  any  of  the  foregoing  experiments  we  leave 
everything  unaltered  except  the  electric  apparatus,  But  substitute 
for  this  one  of  double  the  electromotive  force,  we  shall  in  each 
case  obtain  double  the  deflection — i.  e.,  twice  the  current ;  which 
shows  that  the  current  varies  directly  as  pressure  or 
electromotive  force. 

Professor  Ohm  proved  not  only  that  with  constant  currents  the 


-       B 


FIG.  38.  —  SHOWING  A  SIMPLE  CIRCUIT  CONTAINING  Two  RESISTANCE  WIRES  IN 

PARALLEL. 

current  varies  directly  as  electromotive  force,  and  inversely  as  the 
resistance,  but  also  that  the  current  equals  the  electro- 
motive force  divided  by  the  resistance,  C  =  ^^.  This 
relationship  between  current,  electromotive  force,  and  resistance  is 
known  as  Ohm's  law,  and  this  formula  may  be  written  in  its  equiva- 
lents :  E  =  C  X  R,  or  R  =  |. 


For  these  factors  certain  units  have  been  adopted. 
is  susceptible  of  practical  measurements. 


Each  unit 


The  ohm  is  the  name  given  to  the  unit  of  resistance,  and 
the  standard  unit  is  represented  by  the  resistance  offered  at  the 
temperature  of  melting  ice,  by  a  column  of  pure  mercury  1.06 


UNITS    OF    MEASUREMENT  63 

meters  high,  and  with  a  cross-sectional  area  of  one  square  milli- 
meter ;  or  it  is  about  the  resistance  offered  by  a  copper  wire  -^  of 
an  inch  in  diameter  and  250  feet  long. 

The  ampere  is  the  name  given  to  the  unit  current,  and  it  is 
the  current  that,  flowing  through  a  solution  of  silver  nitrate,  will 
deposit  0.001118  gram  of  silver  in  one  second,  or  in  flowing 
through  water  will  free  0.0000105  gram  of  hydrogen  in  one 
second.  (In  medical  work  we  use  as  the  unit  -j-^nF  ampere,  or 
one  milliampere.) 

The  volt  is  the  name  given  to  the  unit  of  pressure  of  electro- 
motive force,  and  it  is  that  pressure  that,  acting  steadily  upon 
a  conductor  whose  resistance  is  one  ohm,  will  produce  a  current 
of  one  ampere.  The  volt  is  very  nearly  the  electromotive  force 
of  a  zinc-copper  or  a  Daniell  cell.  Expressed  in  these  units,  Ohm's 
law  would  read  :  Amperes  —  ^°]ls  . 

Ohms 

The  coulomb  is  the  unit  of  quantity.  It  represents  the 
quantity  of  electricity  necessary  to  set  free  from  water,  electrolyti- 
cally,  0.010384  milligram  of  hydrogen.  The  coulomb  maybe 
entirely  neglected  and  the  ampere  alone  used,  if  we  consider  the 
time  in  which  a  certain  number  of  co  ulombs  flow.  We  then 
speak  of  an  ampere-hour,  which  means  one  ampere  flowing 
for  thirty-six  hundred  seconds.  One  ampere-hour  is  equal  to 
3600  coulombs,  or  a  current  has  one  ampere  strength  when  it 
gives  one  coulomb  in  one  second.  With  these  facts  in  mind 
we  may  also  use  the  ampere,  which  is  really  only  a  measure  of 
strength,  as  a  measure  of  quantity,  and  then  an  ampere  is  the 
volume  of  current  that  a  pressure  of  one  volt  will  push 
through  a  resistance  of  one  ohm.  I  ampere  =  f 


In  order  to  make  these  units  still  more  easily  understood,  let  us 
compare  them  with  the  unit  used  for  ordinary  fluids,  such  as  water. 
We  measure  water  by  gallons.  This  corresponds  to  the  cou- 
lomb. A  gallon  of  water  is  always  a  gallon,  be  it  under  pressure, 
in  motion,  or  at  rest.  The  same  applies  to  a  coulomb.  The  cou- 
lomb, as  the  gallon,  is  the  absolute  unit  of  quantity. 


64  DYNAMIC    ELECTRICITY 

Now,  supposing  we  have  our  gallons  of  water  under  pressure  in 
a  tank  provided  with  an  outlet,  so  that  a  regular  flow  is  caused  ; 
this  would  give  us  a  current  of  water.  Similarly  an  electric 
current  is  electricity  in  motion. 

Let  us  suppose  that  a  gallon  of  water  is  delivered  each  second  at 
the  outlet  of  the  tank.  This  would  correspond  to  the  ampere,  for 
the  ampere  means  a  flow  in  which  one  coulomb  is  delivered 
in  one  second. 

If  we  lead  the  water  through  a  pipe,  it  encounters  a  certain 
resistance,  greater  or  less  as  the  pipe  is  small  or  large.  The 
conducting  wire  in  electricity  is  analogous  to  the  pipe  in  our 
water-flow,  and  the  unit  of  resistance  is  an  ohm. 

To  overcome  this  resistance  in  such  a  manner  as  to  cause  a  flow 
(or  current)  that  will  deliver  a  certain  quantity  of  water  in  a 
certain  time  requires  a  certain  pressure  or  motive  force. 
If  the  pressure  in  our  tank  of  water  be  such  as  to  deliver  in  each 
second  unit  quantity  (one  gallon)  against  unit  resistance,  we 
have,  further,  a  unit  of  pressure  ;  and  this  is  the  analogue  of  our 
unit  of  electromotive  force,  namely,  the  volt.  Thus,  if  against 
a  resistance  of  one  ohm  we  have  delivered  a  current  of  one 
ampere,  that  is  to  say,  one  coulomb  a  second,  it  indicates  the 
necessary  pressure  in  our  current  source  ;  namely,  that  of  an  elec- 
tromotive force  of  one  volt. 

Having  Ohm's  law  in  mind,  it  is  easy  to  ascertain  the  voltage 
required  to  produce  any  required  current  in  a  wire  of  given  resis- 
tance ;  thus  : 

1.  If  we  have  a  wire  of  2  ohms  resistance,  what  voltage  is 
required  to  obtain  a  current  of  18  amperes? 

F  F 

C  =  — ,  i8  =  -=iSX2  =  E  .".£  =  36. 

Therefore  we  require  36  volts. 

2.  If  we  have  a  resistance  of  ^  ohm  and  require  a  current  of 
200  amperes,  what  voltage  must  we  have? 

t- 

200  =  —  =  200  X  ~  =.  E    . '  .  E  =  50. 
Thus  we  require  50  volts. 


COMPOUND    CIRCUITS  65 

Compound  Circuits. — It  is  only  necessary,  further,  to  remem- 
ber that  when  conductors  are  joined  in  series, — i.  e.,  one  to  the 
other,  lengthwise, — the  total  resistance  is  increased  in  pro- 
portion to  the  sum  of  the  separate  resistances,  and  therefore  the 
current  is  proportionally  diminished;  but  if  they  are  placed 
in  parallel,  the  sectional  area  is  increased,  the  resistance  pro- 
portionally diminished,  and  the  current  is  increased.  When 
a  circuit  has  two  or  more  branches,  it  is  termed  a  divided  or  com- 
pound circuit. 

Thus  if  two  conductors,  A  B,  C  D  (Fig.  39),  each  of  10  ohms 
resistance,  be  connected  as  shown  in  the  illustration,  they  are  said 
to  be  in  parallel,  and  the  joint  resistance  of  the  pair  will  be  ^-, 
or  5  ohms.  Similarly  if  three  such  wires  be  connected  in  parallel, 
their  joint  resistance  would  be  ^-,  or  3.333+  ohms,  and  so  on  for 
any  number  of  parallel  wires.  The  current  in  such  a  parallel 


C  D 

FIG.  39.— SHOWING  Two  RESISTANCE  WIRES  PLACED  IN  PARALLEL. 

arrangement  will  divide  itself  between  the  branches,  as  shown  by 
the  arrows,  and  this  law,  which  governs  the  position  of  current  in 
a  compound  closed  circuit,  is  one  of  great  importance. 

Shunts. — If  a  current  can  flow  through  several  paths,  as  when, 
for  instance,  the  poles  of  a  battery  are  connected  to  several  wires, 
the  current  will  divide  itself  according  to  a  law  of  Kirchhof 
(mathematically  demonstrable,  but  upon  whose  demonstration  it  is 
not  necessary  to  enter),  so  that  the  strength  of  each  branch 
current  is  inversely  proportional  to  the  resistance  of  its 
branch  circuit;  or,  to  express  this  in  a  different  manner,  a  branch 
conductor  that  is  joined  to  a  main  conductor  carries  current  in 
direct  proportion  to  the  relation  that  its  own  conductivity 
bears  to  the  conductivity  of  the  main  conductor.  Thus,  if  the  con- 
ductivity of  the  main  conductor  be  two  and  that  of  the  secondary 
5 


66 


DYNAMIC    ELECTRICITY 


conductor  be  eight,  the  joint  conductivity  will  be  ten.  Ten  parts 
of  current  will  flow  through  both  conductors — two  through  the 
main  and  eight  through  the  secondary  conductor.  Such  a  sec- 
ondary or  branch  conductor  when  introduced  into  a  circuit  is 
called  a  shunt,  and  the  circuit  determined  by  it  is  called  a  shunt 
circuit. 

Variation  of  Current  in  Branches  of  Compound  Circuits. — 
If  the  conductivity  of  one  of  the  conductors  forming  a  compound 
circuit  be  varied,  the  current  flowing  through  each  of  them  will  be 
varied  in  proportion  to  the  resistance  thus  interposed — i.  e., 


FIG.  40. — SHOWING  THE  PRINCIPLE  OF  THE  SHUNT  AS  APPLIED  TO  WATER. 

decreased  in  the  one  of  augmented  resistance,  and  increased  in  the 
others. 

This  will  become  clear  if  we  again  have  recourse  to  the  analogy 
of  the  system  of  water. 

From  figure  40  it  will  readily  be  seen  that  the  water  from  the 
tank  will  flow  through  the  main  and  the  joined  pipe  proportion- 
ately to  their  conductivity  if  the  stop-cock  be  open ;  and  corre- 
spondingly as  the  stop-cock  is  closed  in  the  main  (its  conductivity 
lessened,  i.  e.t  its  resistance  increased),  less  water  will  flow  through 
it,  and  more  through  the  joint  or  shunt.  The  principle  is  of  the 
highest  importance  in  electrotherapeutics,  as  it  governs  the  regula- 
tion of  current  strength  in  many  applications  to  the  human  body, 
especially  when  street  currents  are  used. 


SHUNT    CIRCUITS 


Experimentally,  this  law  may  easily  be  demonstrated  to  apply  to 
a  current  of  electricity  in  the  following  manner:  let  B  (Fig.  41) 
represent  the  battery,  whose  flow  of  current  is  limited  to  about  100 
milliamperes,  and  from  which  a  divided  conductor  carries  the  cur- 
rent over  D  to  the  rheostat  R  and  to  the  human  body  R'.  A  gal- 
vanometer is  introduced  in  each  of  the  divided  circuits  B  D  R  E 
and  B  D  R'  E.  If  the  resistance  in  R  be  made  equal  to  that  of 
R',  the  galvanometer  will  indicate  that  the  currents  in  both  circuits 

B    100  ma. 


N92 


FIG.  41. — SHOWING  THE  PRINCIPLE  OF  THE  SHUNT  AS  APPLIED  TO  ELECTRICITY. 

are  equal.  Assuming  the  equal  resistances  to  be  3000  ohms,  then 
if  we  increase  the  resistance  in  R  to  4000,  5000,  etc.,  the  galvanom- 
eters will  indicate  that  the  currents  in  R  and  R'  have  become  as 
3  :  4,  3  :  5,  etc.  ;  or  if  we  diminish  the  resistance  in  R  to  1000, 
500,  etc.,  the  currents  will  have  become  as  3  :  i,  3  :  0.5,  etc.  In 
other  words,  as  the  resistance  in  R  is  increased,  the  current  in  R' 
is  likewise  increased,  the  electricity  seeking  the  path  of  least 
resistance.  Similarly,  diminution  of  resistance  in  R  diminishes  the 


68  DYNAMIC    ELECTRICITY 

portion  of  current  that  will  pass  through  R'.     In  both  instances 
the  resistance  of  R'  is  presumed  to  be  unaltered. 

If,  finally,  we  introduce  another  galvanometer  into  the  un- 
branched  circuit  B  D  E,  it  will  be  found  that  the  current  herein  is 
equal  to  the  sum  of  the  current  strengths  in  the  branches. 

Temperature  and  Resistance. 

We  have  seen  how  the  total  resistance  of  the  circuit  is  made  up, 
but  we  must  also  consider  its  variability.  As  all  conductors  are 
heated  by  the  passage  of  a  current  through  them,  the  most  im- 
portant factor  in  the  variability  of  resistance  is  heat.  In  some 
cases  the  raising  of  the  temperature  increases  the  resistance  of  a 
conductor  ;  in  other  cases  it  diminishes  the  resistance.  The  resis- 
tance of  metals  becomes  raised  when  their  temperature  is  increased, 
while  that  of  liquids  and  of  nonmetallic  substances  generally  be- 
comes reduced.  In  a  general  way  it  may  also  be  stated  that  the 
greater  the  specific  resistance  of  a  body,  the  more  will  the  tempera- 
ture be  increased  in  it  by  the  passage  of  a  current  and  thus  reduce 
its  resistivity. 

Arrangement  of  Cells. — With  Ohm's  law  before  us  we  can 
easily  understand  how  electromotive  force  may  be  modified  by  the 
arrangement  of  a  number  of  cells,  and  also  what  arrangement  of 
cells  is  best,  in  order  to  obtain  the  greatest  strength  of  current  with 
a  given  external  resistance. 

The  following  table  may  be  taken  as  an  approximation  of  the 
electromotive  force  of  the  various  cells  : 

Daniell, 1.07  volts 

Leclanche, 1.60      " 

Grove, 1.96      " 

Bunsen, 1.96      " 

Bichromate, 2.14      " 

If  it  be  desired  to  obtain  the  greatest  electromotive  force 
from  the  cells  at  our  disposal,  they  must  be  so  connected,  by  j  oin- 
ing  the  unlike  plates  of  successive  cells,  that  the  electromotive 
force  of  each  cell  will  be  added  to  that  of  the  preceding  one,  as 
in  figure  42.  Here  the  zinc  or  -f-  element  of  the  first  cell  is  con- 
nected with  the  copper  or  —  element  of  the  second  cell,  and  the 


ARRANGEMENT    OF    CELLS  69 

zinc  of  the  latter  is  joined  to  the  copper  of  the  third  cell  ;  the  cop- 
per of  the  first  cell,  and  the  zinc  of  the  third  cell,  being  left  free  to 
carry  the  conducting  wires  terminating  in  the  -j-  and  —  poles, 
respectively.  Cells  so  arranged  are  said  to  be  in  series ;  their 
respective  resistances  are  joined  lengthwise  and  thus  added  to  each 
other.  If  E  represents  the  electromotive  force  of  one  cell,  then  3  E 
represents  the  electromotive  force  of  the  three  cells  figured,  and  n 
E  represents  the  electromotive  force  of  n  cells  similarly  connected. 
The  total  resistance  of  a  circuit  being  made  up  of  the  resistance 
of  the  cells  (internal  resistance)  and  the  resistance  of  the  path 
(conducting  wires  and  objects  interposed)  between  the  terminal 
plates  outside  of  the  battery  (external  resistance),  let  us 
represent  the  former  by  r  and  the  latter  by  R ;  then  Ohm's  law 
would  read  C  =  ^-. 


FIG.  42. — CELLS  ARRANGED  IN  SERIES. 

But  if  r  be  the  resistance  of  one  cell  and  E  be  the  electro- 
motive force  of  one  cell,  while  R  represents  the  resistance  of 
the  entire  external  circuit,  we  must,  when  a  number  of  such  cells 
are  in  series,  speak  of  n  E  and  n  r,  so  that  the  formula  would 
read  :  C  =  "E  ;  or,  to  put  this  in  figures,  if  the  electromotive 
force  of  a  single  cell  be  two  volts  and  its  resistance  be  five  ohms, 
while  the  resistance  of  the  external  circuit  is  made  up  of  a  short 
thick  wire  of  practically  no  resistance,  then  the  current  obtained 
would  be  equal  to  C  =  E,  C  —  -,  or  |-  ampere.  If,  now,  we 
take  ten  such  cells  and  join  them  in  series,  the  current  through 
the  same  external  resistance  would  be  C  =  j^r  =  |^,  or  ^  of  an 
ampere,  the  same  as  with  one  cell.  Thus  we  see  that  the  connection 
of  cells  in  series  adds  to  the  internal  resistance  of  the  bat- 
tery, and  that  with  a  negligible  external  resistance  we  obtain  thereby 


DYNAMIC    ELECTRICITY 


no  increase  of  current.  If,  however,  instead  of  no  external  resistance 
we  take  a  large  external  resistance,  —  for  instance,  a  portion  of  the 
human  body  of  say  1000  ohms,  —  the  one  cell  would  give  us 


C  — 


5+  1000 


=     -,  or  about 


ampere,  when  ten  cells  would  give 


10X2 


=  IcSo'  or  about  TTO-  ampere, 


(ID  X  5)  +  i°°° 

With  a  large  external  resistance,  the  addition  of 
various  small  internal  resistances  becomes  almost 
negligible. 

To  obtain  the  greatest  volume  of  current  from  a  given  num- 
ber of  cells  in  short  circuit  a  different  arrangement  is  necessary. 
All  that  has  previously  been  said  about  resistance  is,  of  course, 
applicable  to  internal,  as  well  as  to  external,  resistance.  In  the 
one,  as  in  the  other,  increasing  the  sectional  area  of  a  conductor 


py  py  py 

*»-. — *-•'    ^^_^^    ^__--^ 

FIG.  43. — CELLS  ARRANGED  IN  PARALLEL. 


decreases  the  resistance.  If  this  area  be  doubled,  the  resistance 
will  be  reduced  one-half.  We  could,  therefore,  by  doubling  the 
size  of  a  cell, — that  is,  doubling  the  size  of  the  elements  and 
the  quantity  of  fluid, — halve  the  internal  resistance  of  such  a  cell. 
The  same  result  can  be  obtained  by  joining  the  similar 
plates  of  two  or  more  cells.  Thus  if,  as  in  figure  43,  we  join 
the  carbons  of  three  cells  by  wires  of  practically  no  resistance,  and 
join  the  zincs  in  the  same  way,  the  three  cells  so  joined  will  act 
as  one  cell  of  threefold  size  (see  also  Fig.  44),  having, 
therefore,  an  electromotive  force  of  only  one  cell,  but,  on  the  other 
hand,  having  but  one -third  the  resistance  of  one  cell.  Cells 
so  arranged  are  said  to  be  in  parallel. 

Taking  the  figures  already  made  use  of,  a  cell  of  two  volts  with 
an  internal  resistance  of  five  ohms,  and  with  practically  no  external 
resistance,  would,  as  we  have  seen,  give  us  %  of  an  ampere.  If, 


ARRANGEMENT    OF    CELLS  71 

now,  taking  ten  such  cells,  instead  of  joining  them  in  series  we 
join  them  in  parallel,  the  current  obtained  would  be  that  of  one 
cell  having  one-tenth  the  internal  resistance ;  or  C  —  -£  =  -|  =  4 

To  5 

amperes,  against  %  of  an  ampere  obtained  by  joining  the  same- 
ten  cells  in  series. 

Under  the  same  circumstances,  with  an  external  resistance  of 

1000    ohms   we    should,  however,   obtain    C  = ^~~JL»   or  onty 

about  -5-^-5-  of  an  ampere,  against  ^  of  an  ampere  obtained  by 
joining  them  in  series.  Therefore,  as  joining  cells  in  parallel  di- 
minishes the  internal  resistance  but  does  not  increase  the  electro- 


FIG.  44. — DIAGRAM  OF  CELLS  ARRANGED  IN  PARALLEL. 

motive  force,  the  current  strength    in    such  an  arrangement  will 
vary  inversely  as  the  external  resistance. 

These  methods  of  joining  cells  may  be  combined  in  various 
ways,  and  thus  the  electromotive  force  and  the  internal  resistance 
be  altered.  Such  combination  is  called  multiple  series.  A  good 
practical  rule  for  obtaining  the  greatest  current  from  a  given  num- 
ber of  cells  in  a  given  case  is  so  to  group  the  cells  that  the 
internal  resistance  of  the  battery  approximates  as 
closely  as  possible  the  resistance  of  the  external 
circuit. 


CHAPTER  IV 
EFFECTS  OF  THE  ELECTRIC  CURRENT 

Physical,  Chemical,  and  Physiologic  Effects.  Electrolysis.  Polarization. 
Electromagnetic  Effects.  Magnetic  Field.  Electric  Osmosis.  Thermic 
Action.  Induction.  Measurement.  Voltameter.  Ammeter.  Voltmeter. 
Resistance  Coils.  Wheatstone  Bridge.  Ohmmeter. 

All  currents,  no  matter  what  their  source,  produce  the  same 
effects,  namely,  physical,  chemical,  and  physiologic.  As 
most  of  these  effects  can  best  be  studied  with  the  dynamic  currents, 
we  shall,  notwithstanding  that  some  of  them  have  already  been 
alluded  to,  describe  them  here  in  full,  with  the  exception  of  the 
physiologic  effects,  which  will  be  treated  of  in  that  part  of  the  book 
devoted  to  el^ctrophysiology  and  electropathology. 

The  chemical  effects  are  those  of  electrolysis  and  polari- 
zation. The  physical  effects  are  magnetic,  mechanical, 
thermic,  and  dynamic. 

Chemical  Effects  of  the  Galvanic  Current. 

I.  Electrolytic  Effects. — Faraday  gave  the  name  electroly- 
sis to  the  chemical  decomposition  caused  by  electricity,  and  called 
the  body  that  is,  or  that  is  to  be,  decomposed,  the  electrolyte,1 
and  the  products  of  such  decomposition,  ions.  Hence  that  part 
of  the  electrolyte  that,  through  decomposition,  arises  at  the  posi- 
tive pole  is  called  the  anion,  and  that  found  at  the  negative  pole, 
the  k  at  ion.  As  a  result  of  numerous  experiments,  Faraday  con- 
cluded that  the  quantity  of  electrolyte  decomposed  is  directly  pro- 
portional to  the  strength  of  the  current.  Upon  this  is  based  the 
voltameter. 

In  the  chemical  decomposition  of  water,  hydrogen  is  given  off 

1  This  term  "  electrolyte ' '  must  not  be  confounded  with  the  term  previously  applied 
to  battery  fluid.  The  latter  is  the  active  agent  in  producing  electricity,  while  the  former 
is  acted  upon  passively.  Both  are  broken  up  chemically,  but  the  circumstances  of  the 
electrolysis  differ. 

72 


CHEMICAL   AND    MAGNETIC    EFFECTS  73 

at  the  negative  pole,  or  kathode,  oxygen  at  the  positive  pole,  or 
anode.  In  general,  acids  go  to  the  anode,  while  alkalies  and 
bases  go  to  the  kathode. 

2.  Polarization  Effects. — In  close  relationship  to  the  electrolytic 
effects  of  the  current  stand  its  polarizing  effects.  In  the  organ- 
ism and  in  pieces  of  animal  tissue,  at  the  moment  of  breaking  the 
galvanic  current,  secondary  or  polarization  currents  arise,  and  their 
presence  can  be  demonstrated  by  delicate  indicating  instruments. 
These  currents  are  opposed  to  the  original  currents.  They  are 
undoubtedly  analogous  to  the  polarization  currents  arising  in  inor- 
ganic substances. 

Magnetic    Effects    and     Magnetic    Field    of    the    Galvanic 

Current. 

If  the  wire  through  which  the  galvanic  current  is  flowing 
be  strewn  with  iron  filings,  these  filings  will  remain  attached  to 
the  wire  as  to  a  magnet.  If  a  straight  wire  through  which  a 
galvanic  current  is  flowing  be  brought  near  to  a  magnetic  needle, 
above  or  below  it,  but  parallel  to  its  position  of  rest, — that  is,  in 
the  magnetic  meridian, — the  needle  will  be  deflected  from  its  position 
of  rest,  and  will  tend  to  take  up  a  position  at  a  right  angle  to  that  of 
rest  and  that  of  its  deflecting  circuit. 

The  direction  in  which  the  needle  will  be  deflected  may  always 
be  predetermined  according  to  Ampere's  rule,  which  says: 
'  Imagine  yourself  swimming  in  the  electric  current,  so  that  the 
direction  of  the  current  is  from  the  feet  to  the  head,  and  that  your 
face  be  turned  toward  the  needle ;  then  the  pole  of  the  needle 
that  points  to  the  north  will  always  be  deflected  in  the  direction  of 
the  extended  left  hand  of  the  swimmer.'  (See  Figs.  45,  46,  47.) 

At  the  same  time  that  Ampere  formulated  the  foregoing  rule  for 
recognizing  the  deflecting  direction  of  the  current,  he  furthermore 
proposed  to  utilize  the  arc  of  deflection  of  the  needle  for  the  meas- 
urement of  current  strength,  and  called  the  apparatus  that  renders 
this  possible,  a  galvanometer. 

Magnetic  Field. — We  know,  from  practical  experience,  that  a 
magnet  acts  upon  a  piece  of  soft  iron  or  upon  a  magnet  placed  at  a 
distance,  by  attraction  or  repulsion.  Whereas  formerly  it  was  as- 


74 


EFFECTS    OF   THE    ELECTRIC    CURRENT 


FIG.  45.—  ILLUSTRATING  AMPERE'S  RULE  OF  THE  DEFLECTION  OF  A  MAGNETIC 

NEEDLE. 


FIG.  46. — ILLUSTRATING  AMPERE'S  RULE  OF  THE  DEFLECTION  OF  A  MAGNETIC 

NEEDLE. 


FIG.  47.— ILLUSTRATING  AMPERE'S  RULE  OF  THE  DEFLECTION  OF  A  MAGNETIC 

NEEDLE. 


MAGNETIC    EFFECTS  75 

sumed  that  this  action  was  due  to  the  creation  of  an  attraction  or 
repulsion  force  at  a  distance,  it  is  now  assumed  that  by  its  mere 
presence  a  magnet,  in  some  way  of  which  we  are  ignorant,  modifies 
the  surrounding  medium.  Theoretically,  this  modification  covers 
an  infinite  distance,  but  practically,  its  distance  is  limited  and  the 
extent  is  governed  by  the  strength  of  the  magnet.  The  extent  of 
the  medium  so  modified  is  called  the  magnetic  field.  A  small 
magnetic  needle,  suspended  by  a  silk  thread  so  as  to  swing  freely 
and  horizontally,  will,  if  brought  into  a  magnetic  field,  be  deflected 
from  its  north-south  position  with  more  or  less  rapidity,  and  in  a 
different  direction,  according  to  the  position  of  the  field  in  which  it 
is  placed — that  is,  according  to  the  direction  and  intensity  of  the 
force  that  impels  it  to  leave  its  position  of  rest.  If  such  a  needle 
be  successively  placed  at  each  point  of  a  magnetic  field,  the  direc- 
tion and  intensity  of  the  magnetic  force  at  each  point  may  be  deter- 
mined. By  agreement,  therefore,  the  magnetic  field  is  represented 
by  curved  and  by  straight  lines,  which  have  been  obtained  by 
making  them,  at  each  point,  take  the  direction  that  the  magnetic 
needle  would  take  if  placed  at  that  point ;  furthermore,  these  lines 
are  so  arranged  that  at  each  point  their  distance  from  adjoining 
lines  is  inversely  proportional  to  the  magnetic  action  at  this  point ; 
so  that  the  greater  the  magnetic  action,  the  closer  do  the  lines  ap- 
proach one  another.  This  is,  of  course,  a  purely  conventional  mat- 
ter, for  there  should  be  a  line  for  every  point  in  the  space  surround- 
ing the  magnet.  These  lines  are  designated  as  lines  of  force. 

Electromagnets. — The  knowledge  of  magnetic  properties  of  a 
circuit  is,  however,  considerably  older  than  that  just  detailed.  Fully 
twenty  years  prior  to  the  discovery  of  the  deflection  of  a  magnetic 
needle  by  the  galvanic  current,  it  was  known  that  a  piece  of  iron 
introduced  into  a  galvanic  circuit  for  a  long  period  of  time  finally 
became  magnetic.  If  a  copper  wire  is  wound  around  a  cylinder  of 
wood  or  pasteboard  so  that  each  turn  of  wire  is  well  insulated  from 
the  adjoining  turns,  and  in  the  hollow  of  such  a  spiral  a  solid  cyl- 
inder of  soft  iron  is  introduced,  then  this  iron  becomes  magnetic 
when  the  current  flows  through  the  surrounding  wire,  losing  its 
magnetism  when  the  current  ceases.  Such  a  magnet  is  called  an 
electromagnet. 


76  EFFECTS  OF  THE  ELECTRIC  CURRENT 

Mechanical  Effects  of  the  Electric  Currrent. 

In  the  circuit,  the  mechanical  effects  of  the  galvanic  current 
are  of  a  molecular  or  of  a  molar  nature.  The  molecular 
effects  become  evidenced  mostly  by  structural  changes  in  the 
traversed  conductor ;  thus,  copper  wires  that  are  frequently  tra- 
versed by  a  current,  in  time  have  their  conductivity  altered.  The 
molar  action  of  galvanic  electricity  is  shown  by  electric  osmosis 
— the  transfer  of  fluids,  through  porous  partitions,  from  anode  to 
kathode  (cataphoresis). 

Calorific  Effects  of  the  Electric  Current. 

The  thermic  actions  of  the  galvanic  current  have  already  been 
alluded  to.  If,  in  the  circuit  of  a  battery  of  low  resistance,  one 
whose  cells  are  joined  in  parallel,  a  fine  platinum  wire  be  intro- 
duced, the  wire  will,  upon  traversal  of  the  current,  become  heated 
to  a  glow.  The  quantity  of  heat  thus  developed  in  a  circuit  in  a 
certain  time  has  been  found  proportional  to  the  resistance  of  the 
current  circuit  and  to  the  square  of  the  current's  strength. 

It  is  necessary,  however,  to  mention  here,  in  connection  with 
calorific  effects,  that  if  two  points  of  different  potential  be  con- 
nected by  a  wire  conductor  and  this  wire  be  consequently  traversed 
by  a  current  of  electricity,  heat  is  produced,  which  manifests  itself, 
more  or  less,  by  an  increase  of  temperature  in  the  conductor.  This 
effect  ceases  almost  immediately  if  an  electric  equilibrium  be  re- 
established, but  it  is  kept  up  if  the  points  connected  be  maintained 
at  different  potentials.  The  heat  thus  produced  may  be  so  great 
as  to  cause  an  incandescence  of  the  wire.  The  degree  of  heat 
produced  will  depend  upon  the  quantity  of  electricity  that  traverses 
the  wire  and  upon  the  resistance  of  this  conductor. 

This  question  of  calorification  is  important  in  galvanocautery 
and  in  lighting. 

Dynamic  Effects  of  the  Electric  Current. 

These  depend  upon  the  fact  that  electric  currents  act  upon  each 
other  or  upon  magnets,  or,  conversely,  that  magnets  act  upon  elec- 
tric currents.  This  subject  will  be  further  elucidated  under  the  head 
of  dynamic  induction. 


ELECTROLYTIC  MEASUREMENT 


77 


MEASUREMENT  OF  THE  ELECTRIC  CURRENT  AND 
MEASURING  INSTRUMENTS. 

As  we  have  already  seen,  there  are  three  prime  quantities  to 
measure  in  the  electric  current — viz.,  electromotive  force,  which 
is  measured  by  the  unit  called  the  volt;  current,  which  is  meas- 
ured by  the  unit  called  the  ampere;  and  resistance,  which  is 
measured  by  the  unit  called  the  ohm. 

For  the  measurement  of  an  electric  current,  various  effects  of  the 
current  may  be  made  use  of:  thus,  a  current  may  be  measured  by 
electrolysis,  by  its  magnetic  action,  and  by  its  calorific  properties. 

Electrolytic  Measurement. 

The  apparatus  that  is  used  to  measure  a  current  by  means  of  its 
electrolytic  action  upon  liquid  is  called  a  voltameter  (not  to  be 
confounded  with   voltmeter),   and   may  consist, 
for  example,   of  a  vessel  containing  acidulated 
water,  in  which  are  two  strips  of  platinum,  the 
lower  end  of  each  being  connected  through  the 
bottom  of  the  vessel  with  a  pole  of  a  battery,  the 
upper  and  free  end  of  each  being  covered  by  an 
inverted  test-tube  that  has  been  filled  with  acid- 
ulated water  prior  to  such  inversion.     (See  Fig. 
48.)     When  the  current  then  flows,  the  gas — 
hydrogen  or  oxygen — formed  at  each  platinum 
strip  collects  in  the  respective  tubes,  forcing  out 
the  water.     In  the  case  here  assumed  one  tube 
fills  with  gas  twice  as  quickly  as   the  other,  be- 
cause water  consists  of  two  parts  of  hydrogen   and  one   part  of 
oxygen  ;  the  ( — )  strip  from  which  hydrogen  is  liberated  gives  off 
twice  the  volume  of  gas  in  a  stated  time  that  the  other  (-{-)  strip 
gives  off  of  oxygen.     No  matter  what  the  composition  of  the  elec- 
trolyte, the  same  quantity  of  electric  current  will  give  rise  to  the 
same  quantity  of  electric  decomposition  in  a  given  time. 

What  we  have  now  measured,  therefore,  is  quantity,  or,  in  other 
words,  coulombs.  If  we  have  10  amperes  flowing  for  one 
minute,  or  i  ampere  for  ten  minutes,  the  quantity  of  electricity 


FIG. 


48.— A  VOLT- 
AMETER. 


78  EFFECTS  OF  THE  ELECTRIC  CURRENT 

will  still  be  registered  the  same — viz.,  600  coulombs.  This 
result  is  easily  arrived  at.  It  will  be  remembered  that  one 
ampere  delivers  one  coulomb  each  second.  Then  in  one 
minute  60  coulombs,  and  in  ten  minutes  600  coulombs,  must 
be  delivered.  Conversely,  10  amperes  deliver  10  coulombs 
each  second;  therefore  in  one  minute  a  current  of  10  amperes 
delivers  60  times  10,  or  600  coulombs. 

Inasmuch  as  the  current  flowing  through  any  section  of  a  circuit 
is  the  same  as  that  flowing  through  any  other  section,  the  following 
electrolytic  laws  may  be  deduced  : 

1.  The  quantity  of  chemical  action  is  the  same  at  all  points  of  a 
circuit. 

2.  The  quantity  of  an  ion  liberated  at  an  electrode  in  a  given 
time  is  proportional  to  the  quantity  of  the  current  passing  in  a 
given  time  (amperes). 

3.  The  weight  of  an  ion  liberated  at  an  electrode  in  a  given  time 
is  equal  to  the  quantity  of  the  current  multiplied  by  the  electro- 
chemical equivalent  of  the  ion. 

Hence  by  this  electrochemical  decomposition  the  coulomb  may 
practically  be  measured,  according  to  the  nature  of  the  electrolyte,  by 
measurement  of  the  quantity  or  of  the  weight  of  the  liberated  i  o  n. 

Measurement  by  Magnetic  Action. 

We  have  seen  that  upon  the  deflection  of  a  magnetic  needle  from 
its  normal  position  by  a  current  of  electricity  depends  the  construc- 
tion of  the  galvanometer,  and  that  such  a  galvanometer  will  not 
only  show  that  a  current  is  passing,  but  will  measure  its  strength 
and  indicate  its  direction.  According  to  Ampere's  law,  it  may 
easily  be  demonstrated  that  if  a  current  pass  above  the  needle,  and 
parallel  to  it,  from  south  to  north,  the  north  pole  of  a  magnetic 
needle  will  be  deflected  to  the  west,  while  if  the  current  flow  in  the 
same  direction,  but  underneath  the  needle,  the  north  pole  will  be 
deflected  to  the  east.  When  the  current  flows  above  from  north  to 
south,  the  north  pole  will  be  deflected  to  the  east,  and  if  it  flows  in 
the  same  direction  below  it,  the  needle  swings  to  the  west.  Ac- 
cordingly, a  current,  passing  through  a  wire  that  encircles  such  a 
magnetic  needle,  which  is  so  balanced  that  it  may  swing  easily,  will 


MAGNETIC    MEASUREMENT  79 

flow  in  one  direction  in  the  part  of  the  wire  above  the  needle,  and 
in  the  opposite  direction  in  the  part  of  the  wire  below  the  needle, 
and,  therefore,  tend  to  deflect  the  needle  in  one  and  the  same  direc- 
tion. Hence  the  encircling  wire  produces  a  summation  of  effects, 
and  causes  the  needle  to  swing  in  one  direction  with  double  the 
force  that  a  current  passing  merely  above  or  below  would  de- 
flect it. 

In  figure  49,  let  a  b  b'  a!  represent  a  wire  through  which  a  cur- 
rent is  flowing  in  the  direction  indicated  by  the  arrows.  It  is  clear 
that  if  the  current  were  flowing  above  and  below  in  the  same  direc- 
tion,— i.e.,  from  a  to  b  above,  and  from  a'  to  b'  below, — the  one 
current  would  oppose  the  other  and  the  needle  would  be  unaffected  ; 
but  as  the  current  below  the  needle  flows  from  b'  to  a',  both  the 
upper  and  lower  parts  of  the  current  must  exert  their  force  upon 
the  needle  in  the  same  direction. 


L 


FIG.  49. — SHOWING  THE  PRINCIPLE  OF  THE  MULTIPLJCATOR. 

This  effect  may  be  increased  by  increasing  the  number  of  turns 
of  wire,  and  it  would  be  directly  multiplied  according  to  the  num- 
ber of  turns,  were  it  not  for  the  fact  that  by  such  an  increase  in 
turns  of  wire  the  resistance  of  the  circuit  is  also  increased.  Such 
an  arrangement  of  turns  around  a  magnetic  needle  is  called  a  tnul- 
tiplicator,  and  upon  this  the  construction  of  the  majority  of  current 
meters  depends. 

The  needle  of  all  such  instruments  is,  however,  influenced  by  the 
magnetism  of  the  earth,  and  this  necessitates  placing  the  instrument 
so  that  the  needle  shall  point  magnetically  north  and  south.  This 
is  often  impracticable,  and  therefore  it  becomes  necessary  to  neutral- 
ize in  some  way  the  effect  of  the  earth's  magnetism  upon  the  needle. 
This  can  be  effected  by  taking  two  similar  needles,  placing  them 
above  and  parallel  to  each  other,  and  connecting  them  rigidly,  so 


8o 


EFFECTS    OF    THE    ELECTRIC    CURRENT 


that  their  poles  point  in  opposite  directions,  as  is  shown  in  figure 
50.  Such  a  pair  of  magnetized  needles  is  called  an  astatic 
system. 


FIG.  50. — AN  ASTATIC  SYSTEM  OF  NEEDLES. 

Perfect  astaticism  is  a  mechanical  impossibility ;  the  majority  of 
such  systems  tend  to  come  to  rest  in  a  more  or  less  east-west  posi- 


FIG.  51. — SHOWING  THE  METHOD  OF  WINDING  COIL  IN  THE  ORIGINAL  FORM  OF 
ASTATIC  GALVANOMETER. 

tion,  just  as  a  very  weak  magnet  would  ;  while  a  perfect  astatic  sys- 
tem should  remain  pointed  in  any  direction  in  which  it  is  placed, 


ASTATIC    GALVANOMETERS 


8l 


without  having  any  tendency  to  alter  its  position.  A  galvanometer 
constructed  with  such  a  system  is  called  an  astatic  galvanometer, 
and  the  system  herein  is  deflected  by  a  current  passing  through  a 
coil,  the  same  as  that  previously  described. 

In  the  instruments  of  older  make,  the  coil  is  usually  so  wound 
that  it  passes  above  and  below  the  lower  needle,  and  only  below 
the  upper  one,  as  is  shown  in  figure  51. 

The  current  through  the  coil  will  act  so  as  to  turn  each  needle 
of  the  system  in  the  same  direction. 

In  more  recent  instruments  both  needles  are  surrounded  by  coils 
of  wire,  so  that  we  have  a  multiplied  effect,  as  is  shown  in  figure  52. 


FIG.  52. — SHOWING  THE  METHOD  OF  WINDING  COIL  IN  IMPROVED  FORM  OF  ASTATIC 

GALVANOMETER. 

The  mirror  galvanometer  is  an  instrument  used  for  the  meas- 
urement of  very  small  currents — currents  so  small'  that  their  read- 
ing upon  the  scale  would  be  difficult  on  account  of  the  slight 
deflection  of  the  needle  ;  and  for  this  purpose  the  principle  governing 
reflected  light  is  made  use  of. 

A  ray  of  light  striking  a  perfectly  plane  mirror  will  be  reflected 
from  the  mirror  at  an  angle  equal  to  the  angle  of  incidence.  A 
very  small  and  light  mirror  is  therefore  attached  to  the  needle  of  a 
galvanometer,  and  moves  when  the  needle  moves.  A  ray  of  light 
made  to  strike  the  mirror  perpendicularly,  when  the  needle  stands 
at  zero,  will  be  reflected  straight  back.  If,  however,  the  needle, 
and  with  it  the  mirror,  be  moved  through  any  angle,  the  reflected 
ray  will  no  longer  be  reflected  perpendicularly,  but  will  be  reflected 

at  an  angle  dependent  upon  the  deflection  of  the  needle.     Thus, 
6 


82 


EFFECTS    OF    THE    ELECTRIC    CURRENT 


if  A  o  B  (Fig.  53)  be  a  semicircular  scale,  and  at  o  there  be  a  small 
hole  through  which  a  ray  of  light  passes  and  falls  perpendicularly 
upon  the  mirror  m  n,  then  the  ray  will  be  reflected  directly  back 


10 


20 


30 


40 


50 


60 


A  B 

FIG.  53. — SCALE  OF  MIRROR  GALVANOMETER. 

through  the  hole  so  long  as  the  position  of  the  mirror  remains 
unchanged ;  if,  however,  the  mirror  be  tilted,  as  shown  in  figure 
54,  the  light  striking  the  mirror  at  an  angle  of  say  20  degrees,  it 


30 


40 


FIG.  54.— SHOWING  COURSE  OF  DEFLECTED  RAY  ON  SCALE  OF  MIRROR  GALVA- 
NOMETER. 

will  also  be  reflected  at  an  angle  of  20  degrees,  and  the  spot  of 
light  will  be  seen  on  the  scale  at  a  point  marked  40. 

The  angular  deflection  of  a  reflected  ray  is  double  that  of  the 
angle  of  the  mirror  that  deflects  it,  and  we  are  thereby  enabled  to 


MIRROR    GALVANOMETERS  83 

divide  the  scale  into  larger  divisions,  and  thus  obtain  a  more 
accurate  reading. 

For  practical  purposes,  especially  for  rapid  reading,  the  oscilla- 
tions of  the  magnetic  needle  must  be  decreased.  Such  a  decrease 
is  obtained  by  damping;  and  instruments  so  damped  are  called 
dead  beat.  The  damping  may  be  effected  in  various  ways  :  as 
by  placing  around  a  needle  pieces  of  copper  or  a  mass  of  copper ; 
or  by  immersing  the  needle  in  a  cell  filled  with  a  liquid ;  or  by 
attaching  wings  of  mica  to  the  needle. 

So,  also,  it  is  often  necessary  to  measure  currents  so  large  that 
the  instrument  would  be  endangered  by  their  use.  To  guard 
against  such  injury  and  to  increase  the  reading  capacity  of  the 
instrument,  a  shunt  is  introduced  ;  that  is  to  say,  another  path  is 
furnished  that  is  parallel  to  the  first  and  through  which  the  current 
may  flow.  The  principle  of  the  shunt  has  already  been,  explained 
(see  derived  or  shunt  currents,  p.  65),  and  according  to  this  prin- 
ciple we  can  arrange  the  resistance  in  the  shunt  so  that  any 
desired  portion  of  the  current  will  pass  through  this,  while  the 
remainder  passes  through  the  galvanometer.  Thus,  for  example, 
if  the  resistance  of  shunt  and  galvanometer  is  made  to  equal  10, 
and  it  is  desired  that  -fa  of  the  current  pass  through  the  shunt  and 
only  -j^  through  the  galvanometer,  then  the  resistance  of  the  gal- 
vanometer must  be  9  times  as  great  as  that  in  the  shunt. 

The  differential  galvanometer  is  an  instrument  so  constructed 
that  its  needle  is  acted  upon  by  two  equal  coils  wound  so  as  to 
oppose  each  other.  When  equal  currents  flow  through  the  coils, 
the  action  of  one  current  neutralizes  the  action  of  the  other,  and 
the  needle  remains  at  rest.  Any  difference  in  the  equality  of  the 
current  strengths  will  cause  a  deflection  that  will,  of  course,  be 
proportional  to  the  inequality. 

Galvanometers  that  are  so  arranged  as  actually  to  measure  the 
current  are  called  amperemeters,  or  this  term  is  contracted  to 
ammeters. 

A  practical  ammeter  must,  of  course,  be  less  delicate  in  con- 
struction than  the  instruments  thus  far  spoken  of,  as  we  must  be  in 
a  position  to  measure  very  large  currents.  The  principles  upon 
which  such  an  instrument  is  constructed  are  very  simple.  Above 


84 


EFFECTS    OF    THE    ELECTRIC    CURRENT 


all,  the  scale  of  the  instrument  must  be  so  divided  that  it  may  be 
read  directly  in  amperes,  every  number  marked  thereon  repre- 
senting an  ampere.  The  further  principles  are  represented  in 
figure  55.  Thus,  let  N  S  represent  a  strong 
permanent  magnet,  between  the  poles  of 
which  a  small  needle,  S  N,  is  suspended  ; 
the  position  of  rest  of  this  needle  will  be 
controlled  by  the  magnet,  while  a  light 
pointer,  carried  by  the  needle,  will  indicate 
its  position  of  rest,  or  zero  mark,  upon  a 
scale  provided  for  this  purpose.  Above 

and  below  the  needle  is  a  coil,  C  C',  through  which  the  current  to 
be  measured  is  made  to  flow.  By  such  a  current  the  needle  will 
be  deflected  from  its  position  of  rest,  and  the  pointer  from  the  zero 
mark  of  the  scale.  The  position  that  the  pointer  occupies  upon 
the  scale  when  I,  2,  3,  4,  etc.,  amperes  of  current  flow  through 
the  coils  may  then  be  marked  accordingly,  and  a  scale  thereby 
calibrated  for  direct  reading. 


FIG.  55. — SHOWING  PRIN- 
CIPLE OF  THE  AMMETER. 


FIG.  56. — AMMETER. 


FIG.  56  A. — ARRANGEMENT 
OF  AMMETER  NEEDLE. 


Various  means  may  be  employed  to  hold  the  needle  in  a  fixed, 
or  zero,  position  ;  a  permanent  magnet,  an  electromagnet,  a  spring, 
or  the  action  of  gravity  is  used  to  accomplish  this. 

A  form  of  ammeter  frequently  used  is  shown  in  figure  56.  A 
short  needle,  N  S,  is  fixed  on  a  shaft,  P  (Fig.  56  A),  which  turns  in 


AMMETERS  8$ 

jewel  cups  and  is  mounted  between  the  poles  of  two  strong  mag- 
nets.    (See  Fig.  57.) 

A  form  of  instrument  that  is  practically  free  from  the  magnetic 
influence  of  the  earth,  and  that  is  extensively  used,  is  the  Weston 
ammeter.  This  instrument  and  its  working  parts  are  shown  in 
figures  58  and  59.  Here  the  coil  C  is  placed  between  the  poles 
of  the  permanent  magnet  M  M  M  M  (only  visible  in  Fig.  58). 
Coil  springs  S  S  hold  the  coil  in  the  zero  position,  and  carry  the 
current  to  be  measured  into,  and  out  of,  the  coil  C.  So  long  as 


FIG.  57. — SHOWING  HOW  THE  AMMETER  NEEDLE  is  MOUNTED.' 


no  current  flows  through  the  coil,  a  pointer,  R,  attached  thereto, 
remains  at  the  zero  point  of  the  scale  ;  so  soon,  however,  as  a 
current  passes  through  the  coil,  the  electromagnetic  action  thus 
set  up  causes  the  pointer  to  move  through  a  certain  distance  upon 
the  scale,  and  this  distance  can  be  read  off  directly,  and  indicates 
the  strength  of  the  flowing  current.  This  instrument  is  usually 
provided  with  a  shunt,  and  then  carries  two  scales,  upon  one  of 
which  the  entire  current  may  be  read,  and  upon  the  other-  the 
portion  that  passes  through  the  shunt.  Either  reading  may  be 


86 


EFFECTS    OF   THE    ELECTRIC    CURRENT 


selected  by  means  of  the  special   mechanism  that  introduces  the 
shunt  or  throws  it  out. 


FIG.  58. — WESTON'S  AMMETER,  SHOWING  WORKING  PARTS. 


FIG.  59.— WESTON'S  AMMETER  COMPLETE. 

Voltmeters. 

In  addition  to  measuring  the  current  strength,  it  is  also 
necessary  to  measure  the  current  pressure,  or  voltage.  The 
instrument  used  is  called  a  voltmeter,  and  although  differing 
from  the  ammeter  in  construction,  need  not  do  so  in  principle. 

For  a  clear  comprehension  of  the  construction  of  a  voltmeter,  it 


MEASUREMENT    OF    PRESSURE  8/ 

is  necessary  to  remember  the  underlying  principle  of  all  measure- 
ment— that  the  means  used  to  measure  must  not  alter  that  which 
is  measured.  As,  however,  all  measuring  instruments  have  some 
resistance,  the  introduction  of  such  an  instrument  into  a  circuit  will 
change  somewhat  the  conditions  that  we  are  dealing  with. 

An  ammeter  must,  in  order  to  be  used,  be  placed  in  the  circuit 
so  that  the  current  will  flow  directly  through  it ;  that  is  to  say,  it 
must  be  placed  in  series  with  the  remainder  of  the  circuit,  and 
therefore  adds  resistance.  If  the  resistance  of  such  an  instrument 
be  large  and  the  resistance  of  the  remainder  of  the  circuit  be  small, 
while  the  pressure  remains  constant,  the  current  obtained  would  be 
materially  lessened.  It  is  therefore  necessary,  in  order  to  measure 
the  real  current  strength,  to  make  the  resistance  of  an  ammeter  as 
small  as  possible  as  compared  with  the  resistance  of  the  remainder 
of  the  circuit. 

Measurement  of  Pressure. 

Pressure  may  be  measured,  in  an  analogous  manner  to  current 
strength,  by  the  differential  or  by  the  comparative  method. 
Thus,  in  the  former  case,  the  difference  between  certain  pressures, 
acting  upon  a  magnetic  needle  through  different  equal  paths,  may 
be  calculated.  In  the  latter  case  the  needle  will  not  be  moved  if 
the  pressures  be  equal  ;  and,  furthermore,  a  certain  unknown  pres- 
sure may  be  determined  if  its  effects  be  compared  with  those  of  a 
certain  known  pressure.  Governing  all  methods  is  the  fact,  which 
must  receive  due  consideration,  that  if  the  outflow  of  the  current  is 
more  rapid  than  the  inflow,  the  pressure,  or  electromotive  force, 
cannot  remain  constant.  Thus,  referring  again  to  the  analogy  of 
water  in  a  tank,  the  pressure  in  the  tank  will  depend  upon  the  height 
of  the  body  of  water  that  it  contains.  Let  the  water  (Fig.  60)  be 
supplied  from  the  top  by  means  of  an  inlet,  and  be  allowed  to  run 
out  at  the  bottom  by  means  of  many  outlets  ;  if  all  the  outlets  be 
open,  the  water  will  escape  more  rapidly  than  it  accumulates,  and 
the  pressure  will  diminish.  It  is  therefore  necessaiy,  in  order  to 
keep  the  pressure  in  such  a  tank  constant,  to  diminish  the  outflow 
and  to  regulate  it  in  accordance  with  the  inflow. 

The  desideratum  is  the  same  with  electricity,  and  the  method 


55  EFFECTS    OF   THE    ELECTRIC   CURRENT 

of  attaining  it  is  the  same.  In  the  case  of  the  water  we  turn  off 
some  of  the  stop-cocks ;  in  the  case  of  electricity  we  introduce  re- 
sistance and  take  a  smaller  current.  The  smaller  we  desire  to  make 
the  current,  the  more  resistance  must  be  introduced  ;  that  is,  in 
order  to  measure  electromotive  force  correctly  we  must  have  a 
small  current,  hence  a  large  resistance.  Practically,  then,  we 
require  an  ammeter  of  large  resistance  in  order  to  measure  electro- 
motive force. 


P    P    P     P     P     P    P 

FIG.  60. — SHOWING  THE  RELATION  OF  PRESSURE  TO  OUTFLOW  IN  A  WATER  TANK. 


The    formula,  C  = 


maybe    translated    into;    current 


varies  directly  as  electromotive  force,  and  inversely 
as  resistance,  so  that  if  electromotive  force  is  in  any  way 
altered,  current  will  be  altered  correspondingly  if  resistance  remain 
unchanged. 

The  resistance  of  an  ammeter  or  a  voltmeter  remains  practically 
constant.  If,  then,  we  take  such  a  voltmeter  (an  ammeter  of  high 
resistance)  and  join  it  by  its  terminals  to  the  two  points  of  a  circuit 
whose  difference  of  potential  we  wish  to  ascertain,  then  C  = 


VOLTMETERS 


89 


the  same  instrument,  joined  similarity  to  any  other  two  points,  will 
give  us  C'  =  — £— ;  both  equations  compared  mean  that  the  in- 
dications of  current  C  C'  will  be  proportional  to  the  differences  of 
E  M  F  and  E'  M'  F',  and  this  difference  will  be  given  in  volts,  if  a 
scale  be  calibrated  for  this  purpose.  If  C'  be  2,  3,  or  4  times  as 
great  or  small  as  C,  then  E'  will  be  2,  3,  or  4  times  greater  or 


smaller  than  E.  What  we  require  to  know,  in  order  to  make  a 
scale,  is  the  E  M  F  "  x"  that  will  give  a  current  "j."  If  we  have  a 
current  2y,  the  pressure  must  be  2  xt  etc. 

While  here,  again,  there  are  many  good  instruments,  the  best 
is,  no  doubt,  the  Weston  voltmeter,  which  is  constructed  upon 


9O  EFFECTS    OF    THE    ELECTRIC    CURRENT 

the  same  principle  as  the  ammeter  of  the  same  name  ;  but  which  has 
a  high  resistance  coil  of  fine  wire  (Fig.  61),  placed  in  series  with  the 
moving  coil,  instead  of  the  shunt  coil  of  low  resistance  placed  par- 
allel to  it.  Here,  also,  two  sets  of  readings  may  be  obtained  by 
winding  the  high  resistance  coil  in  two  sections  of  different  lengths, 
and  hence  having  different  resistances.  Every  instrument  must  be 
adapted  to  the  purpose  for  which  it  is  used,  and  these  or  similar  in- 
struments are  the  ones  best  adapted  for  the  currents  used  in  medicine. 
It  is,  therefore,  unnecessary  to  enter  upon  a  description  of  volt- 
meters essentially  different  in  construction  and  principle. 

Measurement  of  Resistance. 

The  last  quantity,  the  measurement  01  which  we  must  elucidate, 
is  resistance,  the  unit  of  which  is  the  ohm,  represented  by  the 
resistance  of  a  column. of  mercury  1.06  meters  in  height,  with  a 
cross-section  of  I  square  millimeter,  at  the  temperature  of  melting 
ice  ;  or  it  is  represented  by  the  resistance  of  a  copper  wire  -^V  of 
an  inch  in  diameter  and  250  feet  long. 

As  mercury  standards  are  impracticable,  standards  of  some  other, 
usually  a  metallic,  conductor  are  employed.  Such  instruments  are 
called  resistance  coils,  and  they  may  be  made,  according  to  their 
length  and  thickness,  to  represent  any  desired  part  of  an  ohm  or 
any  number  of  ohms.  No  matter  what  materials  are  used,  certain 
basic  principles  must  be  followed  in  the  construction  of  such  a 
resistance  coil. 

1.  Its  resistance  must  be  carefully  measured  by  a  certain  stan- 
dard of  resistance. 

2.  It  must  be  constructed  of  material  whose  resistance  changes 
but  slightly  with  change  of  temperature. 

3.  It  must  be  insulated  from  adjoining  conductors  and  protected 
against  moisture,   and  if  wire  coils  are   used,  the  wire   must  be 
doubled  back  upon  itself,  to  prevent  self-induction. 

The  construction  of  such  a  set  of  resistance  coils  is  best  studied 
with  the  aid  of  a  diagram  (Fig.  62).  A  A  A  A  are  thick  blocks  of 
metal ;  F  is  a  plug  of  metal  that  fits  into  the  conic  holes  bored 
into  the  blocks  A  A  A  A,  and  whose  upper  part  is  of  ebonite. 
The  plate  C  C  covers  and  insulates  the  coils  H  H  H.  These  coils 


RESISTANCE    COILS  9! 

are  made  up  of  wire  so  wound  as  to  double  upon  itself,  in  order  to 
prevent  self-induction.  Each  coil  connects  two  metal  rods  of  suffi- 
cient thickness  to  offer  no  resistance  to  the  current,  and  one  of 
these  rods  is  attached  above  to  the  first  block,  the  second  to  the 
adjoining  block,  etc.  ;  the  first  rod  of  the  second  coil  is  connected 
to  the  distal  end  of  the  second  block,  the  second  rod  to  the  proxi- 
mal end  of  the  adjoining  block,  etc.  The  coil  of  wire  connecting 
each  set  of  rods  has  been  carefully  measured.  These  sets  (coils 
and  rods)  of  known  resistance  may  be  substituted  for  any  unknown 
resistance,  and  the  unknown  resistance  thereby  measured.  It  will 
be  seen  that  if  a  plug  be  introduced  into  any  hole,  the  current 
taking  the  path  of  least  resistance  will  flow  through  the  metal 


U      A    U   U     A      U    kl     A      U   k 

A     D 

^     o 

i  i 
,     , 

i!          i 

1 

o      IT- 

E 

-0- 

-D- 

-D 

0- 

1-          *• 

fc= 

J 

H  H  H 

FIG.  62.— CONSTRUCTION  OF  RESISTANCE  COILS. 

block  in  front  of  the  plug,  through  the  plug  and  the  block  behind, 
thus  throwing  out  the  coil  immediately  below  the  plug  ;  and  that, 
therefore,  the  more  plugs  we  introduce,  the  lower  will  be  the  resis- 
tance of  the  circuit ;  so,  also,  if  no  plugs  be  introduced,  the  entire 
available  resistance  will  be  in  circuit.  By  having  a  sufficient  num- 
ber of  such  coils,  calibrated  from  i  ohm  upward,  we  can,  by  group- 
ing them  in  boxes,  introduce  any  desired  resistance  into  the  circuit. 
By  means  of  only  16  coils,  arranged  as  shown  in  figure  63,  any 
number  of  ohms  from  i  to  1 1,1 10  may  be  introduced. 

Thus,  let  us  take  the  circuit  shown  in  diagram  in  figure  64,  con- 
sisting of  a  battery,  B,  an  unknown  resistance,  R,  and  a  galvanom- 
eter, G.  The  deflection  of  the  galvanometer  needle,  caused  by 


92 


EFFECTS    OF    THE    ELECTRIC    CURRENT 


the  current,  is  first  noted .;  then  the  set  of  known  resistances  is 
substituted  for  R,  and  resistance  coils  are  thrown  out  by  the  inser- 
tion of  plugs,  until  the  galvanometer  needle  gives  the  same  deflec- 
tion as  in  the  first  case.  The  resistance  remaining  in  the  circuit 
will  necessarily  equal  the  resistance  previously  introduced — viz., 


100  200  300  400 


FIG.  63. — ARRANGEMENT  OF  RESISTANCE  COILS. 


FIG.  64. — SHOWING  METHOD  OF  DETERMINING  UNKNOWN  RESISTANCES  BY  SUBSTI- 
TUTION. 

the    unknown    quantity ;   and   the    reading   thus    obtained  is   the 
measure  desired. 

If,  as  may  be  the  case  when  either  a  very  large  resistance  o/  a 
fraction  of  an  ohm  is  to  be  measured,  this  substitution  method 
is  impracticable,  recourse  must  be  had  to  the  method  that  forms 


THE    WHEATSTONE    BRIDGE 


93 


the    basis  of  many  kinds  of  resistance  boxes — viz.,  that   of  the 
Wheatstone  bridge. 

The  law  governing  the  principle  of  the  bridge  is :  "  If  a  cur- 
rent divides  into  two  branches  that  are  connected  by  a  transverse 
conducting  path,  then,  if  there  be  no  current  in  the  transverse 
path  (bridge),  the  resistances  of  the  two  parts  of  one  branch  will  be 
equal  to  the  resistances  of  the  two  parts  of  the  other  branch." 


FIG.  65. — SHOWING  METHOD  OF  DETERMINING  UNKNOWN  RESISTANCES  BY  THE 
WHEATSTONE  BRIDGE. 

Thus  if,  as  is  shown  in  figure  65,  in  the  circuit  BCD  the  cur- 
rent be  divided  at  C  D  into  C  E  D  and  C  F  D,  and,  furthermore, 
the  points  E  and  F  be  connected  by  a  conductor  (bridge),  then  a 
galvanometer  introduced  in  the  bridge  E  F  will,  if  the  parts  C  E 
and  E  D  be  proportional  to  C  F  and  F  D,  show  no  deflection  of 
its  needle  ;  because  the  current  flowing  above  the  needle  is  equal  to 


94  EFFECTS    OF    THE    ELECTRIC    CURRENT 

the  one  flowing  below,  and  their  actions  neutralize  each  other.  If, 
now,  C  E  be  so  constructed  as  to  have  the  same  resistance  as  E  D, 
and  variable  known  resistances  be  introduced  between  D  and  F,  while 
the  unknown  resistance  to  be  measured  is  placed  between  C  and  F, 
then,  when  the  resistance  introduced  into  D  F  equals  the  unknown 
resistance  in  C  F,  the  needle  will  return  to  rest  at  the  zero  point  and 
the  resistance  of  D  F  gives  the  measure  desired. 

The  Wheatstone  bridge  is,  of  course,  the  most  convenient  instru- 
ment with  which  to  measure  resistances  ;  but  it  may  occur  that  the 
resistance  of  a  wire  coil  or  lamp  is  wanted,  while  no  Wheatstone 
bridge  is  to  be  had  to  measure  it.  Under  these  circumstances  a  sim- 
ple method,  dependent  on  Ohm's  law,  can  be  employed.  The  neces- 
sary apparatus  are  the  amperemeter,  the  voltmeter,  and  the 
source  of  current.  It  will  be  remembered  from  Ohm's  law  that 
R  =  ^.  So,  if  we  measure  the  current  before  it  enters  into  our 


FIG.  66.  —  SHOWING  THE  METHOD  OF  DETERMINING  UNKNOWN  RESISTANCES  BY 
MEANS  OF  AN  AMMETER  AND  A  VOLTMETER. 

unknown  resistance  and  then  measure  the  electromotive  force 
after  it  has  encountered  the  resistance,  we  shall  have  two  known 
quantities  for  our  equation  and  can  easily  find  the  unknown  quantity, 
R.  For  example,  let  us  find  the  resistance  offered  by  an  incandescent 
lamp  : 

In  figure  66,  A  represents  the  lamp  of  unknown  resistance, 
introduced  into  our  circuit.  The  arrows  show  the  direction  of  the 
current.  Let  us  introduce  an  amperemeter,  B,  so  as  to  determine 
our  original  current  before  it  enters  the  lamp.  In  order  to  deter- 
mine the  electromotive  force  we  insert  the  voltmeter,  C,  into  the 
circuit,  so  as  to  measure  the  potential  after  the  current  has  en- 
countered the  resistance.  We  now  take  our  reading.  The 
amperemeter  registers  0.50,  and  the  voltmeter  109.50.  Then,  as 


R  ^=  ^,  -  ^,  201.90  ohms  is  the  resistance  offered  by  the  lamp. 


CHAPTER   V 

OTHER  METHODS  OF  OBTAINING  AND  ALTERING 
ELECTROMOTIVE   FORCE 

Dynamic  Induction.    Magnetic  Induction.     Volta-magnetic  Induction  Appa- 
ratus.    Dynamos.     Thermo-electricity.     Thermopile.     Sinusoidal  Current. 

Induction. 

Of  static  induction  we  have  already  spoken,  but  the  induction 
produced  by  means  of  dynamic  and  magnetic  effects  is  gov- 
erned by  entirely  different  laws. 

In  1831  Faraday  discovered  that  a  wire  traversed  by  a  cur- 
rent,  and  suddenly  brought  near  to  another  wire  through  which  no 
current  is  passing,  develops  in  the  second  wire  an  instantaneous 
current  of  electricity.  If  the  wires,  instead  of  being  suddenly  ap> 
proximated,  are  suddenly  separated,  the  same  thing  will  occur.  As 
it  is  the  approach  or  the  withdrawal  of  the  electric  current  in  the 
first  wire  that  sets  up  the  momentary  current  in  the  second  wire,  we 
can  more  conveniently  demonstrate  this  action  by  introducing  or 
removing  an  electric  current  into  or  from  the  first  wire.  This  will 
be  made  plain  by  the  following  illustration  (Fig.  67). 

Let  A  represent  a  galvanic  current  supplied  by  the  current  from 
a  battery,  B,  and  having  at  some  part  a  switch,  S,  that  will  enable 
us  to  introduce  and  throw  out  the  current ;  and  let  C  represent  a 
similar  wire  circuit  placed  parallel  to  A,  and  in  which  is  placed  a 
galvanometer,  G.  If  the  switch  at  S  be  closed,  a  current  will  flow 
through  A  in  the  direction  indicated  by  the  arrows.  At  the  moment 
the  circuit  in  A  is  thus  closed,  the  galvanometer  needle,  which,  while 
at  rest,  occupied  the  north-south  position,  will  be  deflected.  This 
deflection  will  be  to  the  west — that  is,  the  north  pole  of  the  needle 
will  be  turned  to  the  west ;  but  it  will  return  immediately  to  its 
north-south  position,  retaining  this  while  the  current  continues 
to  flow  through  A.  At  the  moment  the  circuit  is  again  broken 
at  S  the  needle  will  again  be  deflected,  but  this  time  in  the  opposite 

95 


96 


ALTERATION  OF  ELECTROMOTIVE  FORCE 


direction,  with  its  north  pole  to  the  east.  Therefore  a  reverse 
current  is  produced  in  Bat  the  moment  the  circuit  is  closed 
in  A,  and  at  the  moment  the  current  is  broken  in  A  a  current  will 
be  generated  in  B  whose  direction  is  the  same  as  the  one  that 
had  existed  in  A. 

This  production  of  momentary  currents  in  a  closed  electric  con- 
ductor, by  making  and  breaking  a  current  in  an  adjoining  galvanic 
circuit,  is  called  electrodynamic  or  voltaic  induction.  The 


FIG.  67. — SHOWING  THE  METHOD  OF  PRODUCING  AN  INDUCED  CURRENT. 


galvanic  current  circulating  in  A  is  called  the  primary  cur- 
rent; the  current  that  is  set  up  in  B,  and  whose  direction  is  oppo- 
site to  the  primary  one,  is  called  the  closure  induction  cur- 
rent;  while  the  current  of  similar  direction  to  the  primary  one  is 
called  the  opening  induction  current.  Increasing  or  de- 
creasing the  current  strength  in  A  will  produce  in  B  the  same 
effects  as  closing  and  opening  the  A  circuit.  If,  furthermore, 
instead  of  making  use  of  an  inducing  galvanic  current  for  the  pro- 
duction of  such  momentary  induced  currents  we  make  use  of  a 


INDUCTION    COILS 


97 


magnet,  approaching  and  withdrawing  it  suddenly  from  B,  the 
same  results  would  be  obtained — viz.,  the  production  in  B  of  cur- 
rents of  opposite  directions  to  each  other.  So,  also,  the  same 
effects  may  be  produced  by  the  magnetization  or  demagnetization 
of  an  iron  core  of  an  electromagnet,  as  well  as  by  increasing  or 
decreasing  the  quantity  of  such  magnetism. 

This  production  of  momentary  electric  currents  in  a  closed  elec- 
tric conductor  by  means  of  the  approach  or  withdrawal  of  adjoining 
magnets,  or  by  the  magnetization  or  demagnetization  of  the  core 
of  an  adjoining  electromagnet,  is  called  magneto-induction. 

In  order  to  produce  an  intensification  of  energy,  the  wire  A  may 


FIG.  68. — AN  INDUCTION  COIL. 


be  wound  around  a  nonconducting  cylinder ;  the  wire  itself  being 
covered  with  silk,  each  turn  of  the  spiral  is  insulated  from  the  ad- 
joining turn.  Over  this  wire  the  second  wire,  B,  also  covered  with 
silk,  is  wound  (Fig.  68). 

The  cylinder  so  wound  with  wire  is  called  an  induction  coil ;  the 
wire  A,  which  is  first  wound  round  the  cylinder  and  in  whose  cir- 
cuit the  current  is  made  and  broken,  is  the  inducing  wire;  the 
wire  B,  in  which  the  momentary  currents  are  set  up  and  from  which 
they  are  collected  for  use,  is  called  the  induced  wire.  The  in- 
ducing wire  and  the  induced  wire  may  each  be  wound  upon  a  sepa- 
rate nonconducting  cylinder,  the  one  being  sufficiently  small  to  allow 
7 


98  ALTERATION  OF  ELECTROMOTIVE  FORCE 

of  its  introduction  into  the  other ;  we  then  have  a  model  according  to 
which  the  sled  induction  ap p a rat-us  is  constructed.  Herewith 
the  strength  of  the  secondary  current  may  be  varied,  for  if  the  sec- 
ondary coil  cover  the  primary  coil  to  its  full  extent,  the  number  of 
turns  of  wire  in  which  induction  takes  place  will  be  greater,  and 
hence  the  current  stronger,  than  if  only  a  part  of  the  primary  coil 
be  so  covered  by  the  secondary  one.  It  will  thus  be  seen  that  by 
increasing  the  number  of  turns  in  the  coils  we  also  increase  the 
strength  of  the  secondary  currents.  Another  method  by  which 
induced  currents  may  be  increased  in  strength  is  the  ingenious 
combination,  already  known  to  Faraday,  of  magneto-  and  volta- 
induction.  This  combination  Faraday  effected  by  introducing  a 
core  of  soft  iron  into  the  primary  spiral.  Upon  the  closure  of  the 
galvanic  current  this  iron  core  becomes  an  electromagnet,  but  upon 
the  opening  of  the  current  the  magnetism  disappears  ;  and  thus 
the  production  and  withdrawal  of  magnetism  in  the  iron  core  act 
inducingly  upon  the  secondary  coil,  in  the  same  manner  as  do  the 
closure  and  opening  of  the  current,  so  that  the  influence  of  the 
primary  coil  becomes  summated,  the  volta-induction  currents  acting 
together  with  the  magneto-induction  ones. 

The  action  of  induction  previously  described  as  taking  place 
between  adjoining  parallel  wires  must,  of  course,  also  take  place 
between  the  adjoining  wires  of  the  primary  coil,  and  this  fact  ex- 
plains the  observation  made  by  others,  but  correctly  interpreted  by 
Faraday,  that  when  a  current  that  is  flowing  through  a  long  wire 
spiral  is  interrupted,  an  opening  spark  is  obtained  that  is  stronger 
than  the  opening  spark  obtained  from  the  source  of  the  induction 
itself,  and  that,  furthermore,  the  longer  the  wire  of  the  spiral,  the 
stronger  is  the  opening  spark.  The  explanation  of  these  phenom- 
ena is  that  the  cessation  of  the  current  in  one  turn  of  the  spiral  pro- 
duces a  similarly  directed  momentary  current  in  the  adjoining  turn  ; 
these  currents  between  the  single  turns  become  added  to  each  other, 
and  produce  the  opening  induction  spark,  which  necessarily  is  the 
greater,  the  more  numerous  the  turns  of  wire  that  make  up  the  spiral. 
This  induction  action  takes  place  not  only  with  the  opening,  but 
also  with  the  closure,  of  the  current,  when  this  induction  current 
that  arises  in  the  primary  coil  is  known  as  the  extra  current, 


MAGNETO-ELECTRIC    MACHINES 


99 


or  primary  induced  current,  in  contradistinction  to  the  sec- 
ondary induced  current  produced  in  the  secondary  coil. 

The  construction  of  an  apparatus  for  the  production  of  a  volta- 
induced  current  can  easily  be  deduced  from  the  foregoing  descrip- 
tion of  the  principles  underlying  the  sled  apparatus,  except  that  in 
addition  to  a  source  of  galvanic  current,  a  primary  coil  with  a  core 
of  soft  iron,  and  a  secondary  movable  coil,  some  mechanism  by 
means  of  which  the  electric  current  can  rapidly  be  made  and 
broken  must  be  employed.  More  will  be  said  in  reference  hereto 
when  we  describe  apparatus  of  an  essentially  medical  nature.  Here 


FIG.  69. — FARADAY'S  MAGNETO-ELECTRIC  MACHINE. 

it  is,  nevertheless,  still  necessary  to  speak  of  the  principles  that 
underly  the  construction  of  a  magneto-induction  apparatus.  The 
essentials  of  such  an  apparatus  are : 

1.  A  magnetic  source  (a  permanent  or  an  electromagnet). 

2.  The  induction  spirals. 

3.  A  mechanism  by  which  the  induction  spirals  may  be  ap- 
proached to  and  withdrawn  from  the  magnetic  source,  or  by 
which  the  latter  may  be  approached  to  or  withdrawn  from  the  former. 

4.  A  mechanism  for  the  collection  of  the  induced  currents 
thus  produced. 


IOO 


ALTERATION  OF  ELECTROMOTIVE  FORCE 


The  approach  and  separation  of  the  magnet  and  coil  may  be 
effected  by  rotating  the  induction  spirals  in  front,  above,  below,  or 
between  the  poles  of  a  horseshoe  magnet,  or  by  rotating  such  a 
magnet  in  front,  above,  below,  or  around  the  induction  spirals. 
The  induction  spirals  may  be  variedly  constructed. 


FIG.  70. — THE  HORSESHOE  INDUCTOR. 

The  earliest  and  simplest  magneto -electric  machine  was 
constructed  by  Faraday.  This  machine  is  shown  in  figure  69. 

One  of  the  oldest  forms  is  the  horseshoe  inductor,  in  which 
the  induction  coils  are  placed  so  as  to  surround  the  ends  of  a  core 
of  soft  iron  bent  in  the  shape  of  a  horseshoe,  as  shown  in  figure  70. 
This  inductor  is  made  to  rotate  below,  behind,  or  in  front  of  the  poles 


THE    DYNAMO  IOI 

of  the  permanent  magnet.  Another  form  of  inductor  is  made  of  a 
cylindric  iron  core  having  a  deep  groove  upon  two  opposite  surfaces, 
in  which  the  wire  of  an  induction  spiral  is  so  wound  that  the  turns 
run  along  the  cylinder  lengthwise,  from  the  groove  of  the  one  sur- 
face to  the  groove  of  the  other.  This  cylindric  inductor  is 
made  to  rotate  between  the  poles  of  the  horseshoe  magnet  in  such 
a  manner  that  its  axis  is  parallel  to  the  arms  of  the  magnet.  Of 
entirely  different  construction  is  the  Gramme  ring  inductor. 

For  gathering  the  current  either  a  collector  or  a  commu- 
tator is  made  use  of;  in  the  first  case  only  alternating  cur- 
rents are  obtained  ;  in  the  second,  unidirectional  ones. 

Without  entering  here  upon  a  detailed  description  of  such 
machines,  it  may  be  stated  that  the  industrial  machines  for  furnish- 
ing current  for  technical  purposes  are,  with  more  or  less  com- 
plication, constructed  essentially  upon  such  a  plan. 

The  modern  dynamo  is  an  apparatus  that  is  unsurpassed  for 
simplicity  of  construction  and  efficiency  in  transforming  one  kind 
of  energy  into  another.  The  dynamo  is  actually  a  reversible  ma- 
chine, which  either  transforms  mechanical  energy  into  electric 
energy,  as  is  the  case  in  the  magneto-machine  just  spoken  of,  or  it 
transforms  electric  energy  into  mechanical  energy.  In  the  first  case 
it  is  called  a  dynamo ;  in  the  second,  a  motor. 

The  simplest  form  of  dynamo  necessarily  gives  an  alternating 
current  and  is  called  an  alternator.  When  supplied  with  the 
piece  of  apparatus  called  the  commutator,  the  current  in  the  prac- 
tical (external)  circuit  is  constant  in  one  direction.  To  such  a 
direct  current  machine  the  term  dynamo  is  restricted  by 
many. 

Currents  from  such  machines  are  now  supplied  from  central  sta- 
tions for  illuminating  purposes,  and  are  available  in  most  houses  of 
large  cities.  Special  consideration  will  be  given  in  another  chapter 
to  the  adaptability  of  these  currents  for  medical  purposes. 

Thermo-electricity. 

A  source  of  electricity  that  has  hitherto  been  impracticable  and 
that  seems  now  to  promise  a  satisfactory  current  supply  for  many 
medical  purposes  is  the  thermo-electric  element. 


IO2 


ALTERATION  OF  ELECTROMOTIVE  FORCE 


A  polished  copper  wire  bent  in  the  shape  of  a  ring,  the  two  ends 
being  connected  with  a  delicate  galvanometer,  will,  if  heated  at  any 
part,  cause  a  deflection  of  the  needle,  thus  showing  that  the  appli- 
cation of  heat  has  produced  a  current  of  electricity  in  the  ring.  If 
such  a  ring  be  made  of  two  different  metals,  by  soldering  them 
together  lengthwise  the  deflection  of  the  needle  will  be  greater  than 
if  the  ring  be  made  of  copper  alone. 


FIG.  71. — THERMO-ELECTRIC  COUPLE. 

If  a  bar  of  bismuth,  B  (Fig.  71),  and  a  bar  of  antimony,  A,  be  sold- 
ered together  at  one  end,  S,  and  the  free  ends  are  joined  by  a  wire, 
a  current  of  electricity  will  flow  through  the  wire  when  the  solder 
is  heated ;  if  the  solder  be  cooled,  a  current  of  opposite  direction 
will  be  created.  A  number  of  such  couples  or  elements  (Fig.  72) 
may  be  joined  together  so  that  a  bar  of  antimony  alternates  with  a 


FIG.  72. — THERMOPILE. 

bar  of  bismuth.  The  intensity  of  the  current  is  thereby  increased, 
a  smaller  quantity  of  heat  causing  deflection  of  the  needle  of  a  gal- 
vanometer in  circuit.  Such  an  arrangement  is  called  a  thermopile, 
or  thermo-electric  battery,  and  the  current  derived  therefrom 
is  termed  thermo-electricity. 


THERMO-ELECTRICITY 


103 


Experiments  made  with  various  combinations  of  metals  show 
that  the  different  metals  may  be  arranged  into  an  electromotive 
series  that  is  governed  by  the  same  laws  as  those  that  govern  a 
voltaic  series.  This  series  is  :  Antimony,  iron,  zinc,  silver,  gold, 
tin,  lead,  mercury,  copper,  platinum,  and  bismuth.  The  antimony 
forms  the  positive,  and  the  bismuth  the  negative,  end  of  the  series. 
In  a  thermocouple  of  antimony  and  bismuth,  which  gives  the 
greatest  difference  of  potential  and  therefore,  other  things  being 
equal,  the  greatest  electromotive  force,  the  current  produced  by 
heating  the  soldered  place  flows  from  the  bismuth  to  the  anti- 


FIG.  73. — THE  NOE  THERMOPILE. 

mony;  that  caused  by  cooling  the  solder  flows  from  the  antimony 
to  the  bismuth. 

The  intensity  of  the  thermocurrent  is  dependent,  aside  from 
the  specific  constituents  of  the  source,  mainly  upon  the  differences 
in  temperature  of  the  two  soldered  ends,  but  also  in  part  upon  the 
absolute  temperature  of  the  two  metals.  Therefore  the  higher  the 
heat  in  the  metals,  and  yet  the  greater  their  difference  of  tempera- 
ture, the  stronger  will  be  the  current  obtained. 

A  practical  form  of  thermobattery,  one  that  has  been  widely 
copied  and  modified,  is  that  constructed  by  F.  Noe,  of  Vienna,  and 


IO4  ALTERATION  OF  ELECTROMOTIVE  FORCE 

known  as  the  Noe  thermopile.  This  pile  is  shown  in  figure 
73.  The  source  of  heat  is  a  Bunsen  flame.  Such  a  battery  of  thirty 
couples  possesses  an  internal  resistance  of  0.4  ohm,  and  an  electro- 
motive force  of  about  2  volts;  thus,  short  circuited,  it  would  furnish 
a  current  of  5  amperes. 

Sinusoidal  Current. 

A  great  deal  of  attention  has  of  recent  years  been  given  to  the 
use  of  the  sinusoidal  current  in  electrotherapy,  and  as  this 
current  is  a  form  of  the  induced  current  that  we  have  just  studied, 
it  will  not  be  amiss  to  speak  of  it  here. 

A  sinusoidal  current  is  an  alternating  induced  current 
in  which  the  electromotive  force  is  so  varied  that  its  rise  and  fall  in 
a  positive  direction  are  immediately  succeeded  without  a  break  by 
an  exactly  corresponding  fall  and  rise  in  the  negative  direction,  and 
this  rise  and  fall  in  both  directions  would,  if  graphically  illustrated, 
describe  a  sine  curve.  This  will  be  better  understood  by  reference 
to  the  pages  that  follow  and  that  deal  with  the  varieties  of  electro- 
motive force. 


CHAPTER   VI 
VARIETIES  OF  ELECTROMOTIVE  FORCE 

Continuous.  Alternating.  Pulsating.  Steady.  Symmetric.  Dis- 
symmetric. Intermittent.  Nonintermittent.  Sinusoidal.  Nonsinusoidal. 
High  Frequency. 

Inasmuch  as  there  is  but  one  electricity  and  the  action  of  elec- 
tricity upon  organic  and  inorganic  substances  varies  according  to  the 
source  from  which  the  electricity  is  obtained,  it  is  necessary  to 
inquire  into  the  causes  of  such  variation. 

These  causes  are  dependent,  first,  upon  the  variations  in  the 
electromotive  force,  which  sets  the  electricity  into  action,  upon 
its  duration,  and  upon  its  direction;  and,  secondly,  upon  the 
other  factors  governing  the  flow  of  current,  quantity,  and 
resistance.  An  examination  of  the  variations  in  duration  and 
direction  of  the  electromotive  force  produced  will  make  clear  the 
characteristics  of  the  different  currents. 

These  currents,  following  Houston  and  Kennelly,  are : 

{Intermittent. 
Nonintermittent. 
(  Steady. 

CURRENTS 

Sinusoidal. 


{Symmetric 
Dissymmetric. 


ALTERNATING  •<  (  Nonsinusoidal. 

(  Dissymmetric. 

Houston  and  Kennelly's  description  is  as  follows  : 

Varieties  of  Electromotive  Force. 

The  voltaic  or  primary  cell  and  the  storage  or  secon- 
dary cell  will  produce  an  electromotive  force  that,  so  long  as 
the  chemicals  remain  unchanged,  does  not  vary  in  strength. 
Such  an  electromotive  force  is,  therefore,  called  a  continuous 
electromotive  force. 

A  continuous  electromotive  force  is  also  obtained  from  a  number 

105 


io6 


VARIETIES    OF    ELECTROMOTIVE    FORCE 


of  other  electric  sources,  such,  for  example,  as  a  continuous 
current  dynamo,  which,  so  long  as  its  speed  of  rotation  remains 
the  same,  produces  an  electromotive  force  that  is  practically  con- 
tinuous. Figure  74  represents  graphically  a  continuous  electro- 
motive force.  The  straight  line  A-S  is  drawn  parallel  to  the  base 
line  o-S,  at  a  distance  representing  i  .  i  volts.  Time  is  measured 
along  the  base  line  o-S,  and  the  fact  that  the  line  A-S  runs  parallel 
to  the  base  line  illustrates  the  constancy  of  the  electromotive  force, 
which  might  be  that  of  a  single  Daniell  cell.  Two  such  cells  con- 
nected in  series  would  produce  an  electromotive  force  of  2.2  volts, 
represented  by  the  straight  line  C—  D,  twice  as  far  above  the  base 
line  as  is  the  line  A-S. 


o 
2.2    C 


1.1       A 


1.1      E 


SECONDS 


FIG.  74. — GRAPHIC  REPRESENTATION  OF  A  CONTINUOUS  ELECTROMOTIVE  FORCE. 

An  electromotive  force  possesses  direction  as  well  as  magni- 
tude ;  that  is  to  say,  it  may  tend  to  send  a  current  through  a  circuit 
in  one  direction  or  in  the  opposite  direction.  All  electromotive 
forces  that  tend  to  send  the  current  in  one  direction  may  be  regarded 
as  positive,  and  all  that  tend  to  send  the  current  in  the  opposite 
direction  as  negative. 

Positive  electromotive  forces  are  represented  graphically  by  dis- 
tances above  the  line  o-S,  and  negative  electromotive  forces  by  dis- 
tances below  it.  Thus,  in  figure  74  the  line  E— F  would  indicate  a 
negative  electromotive  force  of  i.i  volts,  or  an  electromotive  force 
directly  opposed  to  that  of  the  line  A-S.  Figure  75  shows  the 


CONTINUOUS  AND  PULSATORY  CURRENTS 


TO/ 


electromotive  force  produced  by  a  continuous  current  dynamo. 
Here  the  line  A-B  is  parallel  to  the  base,  as  before,  but  instead  of 
being  straight,  is  a  fine  wavy  line.  These  little  waves  represent 


114- 
113- 
112- 
111- 

tO    110 

§109- 

>  108- 

107- 

10&'- 

105. 


8 


SECONDS 


w 


FIG.  75. — GRAPHIC  REPRESENTATION  OF  THE  ELECTROMOTIVE  FORCE  PRODUCED  BY 
A  CONTINUOUS  CURRENT  DYNAMO. 

variations  in  the  quantity  of  electromotive  force  produced  every 
time  that  the  bar  of  the  commutator  passes  underneath  the  electric 
brush.  These  wavelets  exist  in  the  electromotive  force  of  every  con- 


900- 

800- 

700- 

CO     600- 

§     500. 

>     400- 

300- 

200 

100- 


-I- 


u  1  2  3  4  5_  JL  7  8  9 

To       To        10        TO        10        10       10         10       to 

SECONDS 

FIG.  76. — GRAPHIC  REPRESENTATION  OF  A  PULSATORY  ELECTROMOTIVE  FORCE. 


tinuous  current  dynamo.  When  they  are  very  marked,  as  repre- 
sented in  figure  76,  the  electromotive  force  is  said  to  be  pulsatory. 
Such  electromotive  forces  are  produced  by  some  continuous  current 


-i 

m 


• 

IO8  VARIETIES  OF  ELECTROMOTIVE  FORCE 

generators,  usually  for  supplying  arc  lamps.  It  is  evident  that  at 
different  times  the  electromotive  force  varies  considerably  in  its 
magnitude,  but  it  never  changes  direction,  and  the  line  A— B  is 
always  on  one  side  of  the  zero  line  o— S ;  that  is  to  say,  it  has 
always  the  same  direction  in  the  circuit,  just  as  though  a  battery  of 
voltaic  cells  were  employed  to  send  a  current  through  a  circuit,  and 
at  intervals  a  certain  number  of  these  cells  were  cut  out  and  later 
reintroduced. 

When  the  waves  start  each  time  from  the  zero  line,  the  electro- 
motive force  is  said  to  be  intermittent.  Figure  77  shows  that, 
at  certain  periods,  an  electromotive  force  exists  in  the  circuit  in 


• 


B 


TIME 

FIG.  77. — GRAPHIC  REPRESENTATION  OF  AN  INTERMITTENT  ELECTROMOTIVE  FORCE. 

one  direction,  and  that  during  the  intervals  there  is  no  electromotive 
force  whatsoever.  The  intermittent  electromotive  force 
can  be  obtained  by  connecting  a  continuous  electromotive  source — 
e.  g.,  a  voltaic  battery — to  a  wheel  interrupter  in  such  a  manner 
that  the  electromotive  force  will  periodically  be  cut  off  and  applied. 

In  all  the  foregoing  cases,  although  the  strength  of  the  electro- 
motive force  varies  at  different  times,  yet  at  no  time  does  it  change 
direction,  so  that  the  curved  line  lies  wholly  above  the  base  line. 

When  the  electromotive  force  changes  direction  as  well  as 
magnitude,  it  becomes  alternating.  Thus,  in  figure  78  the  elec- 
tromotive force  is  seen  to  alternate  between  10  volts  positive  and 
IO  volts  negative,  the  transitions  in  this  particular  case  being  made 


ALTERNATING    CURRENTS 


IO9 


instantaneously.  Such  an  electromotive  force  may  be  produced  by 
connecting  a  battery  of  voltaic  cells  with  a  current  reverserin 
such  a  manner  that,  by  rotating  the  handle,  the  electromotive  force 


SECONDS 


FIG.  78. — GRAPHIC  REPRESENTATION  OF  AN  ALTERNATING  ELECTROMOTIVE  FORCE. 


FIG.  79. — GRAPHIC  REPRESENTATION  OF  A  GRADUALLY  ALTERNATING  ELECTRO- 
MOTIVE FORCE. 

will  periodically  be  reversed  without  being    withdrawn   from  the 
circuit. 

It  is  not  necessary  that  an  alternating  electromotive  force  should 
change  abruptly  from  its  maximum  positive  to  its  maximum  nega- 
tive value.  In  fact,  in  most  cases  the  change  occurs  in  a  more 


no 


VARIETIES    OF    ELECTROMOTIVE    FORCE 


gradual  way,  as  shown  in  figure  79,  which  illustrates  a  common 
type  of  alternating  electromotive  force. 

Figures  80  and  8 1  represent  the  same  alternating  electromotive 


+  100- 
80 

CO60' 
5   40- 

0   20  - 

0 

-20  • 
-40 
-60  - 
-80  - 
-100- 


FIG.  80. — GRAPHIC  REPRESENTATION  OF  A  GRADUALLY  ALTERNATING  ELECTRO- 
MOTIVE FORCE. 


-100  J 

FIG.  81. — GRAPHIC  REPRESENTATION  OF  A  GRADUALLY  ALTERNATING  ELECTRO- 
MOTIVE FORCE. 

force,  although  the  graphic  appearance  of  the  waves  is  changed, 
owing  to  the  variations  of  the  scale  of  time  along  the  base  and  of 
the  scale  of  electromotive  force  along  the  vertical  line. 


SYMMETRY    AND    DISSYMMETRY 


I  II 


It  will  be  observed  that  in  all  representations  of  alternating  elec- 
tromotive force  there  is  first  motion  in  one  direction,  in  which  the 
electromotive  force  beginning  at  the  base  line,  or  zero,  gradually 
increases  in  value  to  a  maximum,  and  then  gradually  falls  until  it 
again  reaches  zero  ;  then  changes  direction,  going  through  a  like 
rise  and  fall  in  the  opposite  phase.  Each  of  the  waves  o  A  B  or 
B  C  D  is  called  an  alternation. 

Alternating  electromotive  forces  may  be  symmetric 
or  dissymmetric. 

A  symmetric  electromotive  force  (Fig.  82)  is  one  in  which 


+  50  - 

+  40  - 

+  30  - 
O)  +20  - 
>  +10  - 
0 

-  10   - 

-20  - 

-30  - 

-40  - 

-50  - 

FIG.  82.  — GRAPHIC  REPRESENTATION  OF  A  SYMMETRIC  ELECTROMOTIVE  FORCE. 


the  positive  waves  are  the  same  as  the  negative  waves,  except  that 
they  move  in  opposite  directions. 

A  dissymmetric  alternating  electromotive  force  (Fig.  83) 
is  one  in  which  the  positive  wave  differs  from  the  negative,  not 
merely  in  its  direction,  but  also  in  its  outline. 

Symmetric  alternating  waves  of  electromotive  force  are  pro- 
duced by  alternating  current  dynamos,  or  alternators.  Dissym- 
metric alternating  electromotive  force  waves  are  produced  by  par- 
ticular types  of  apparatus,  such  as  faradaic  coils. 

It  is  clear  that  an  electromotive  force  is  alternating  if  it  changes 
its  direction  and  magnitude  periodically,  and  that  considerable  varia- 


112 


VARIETIES    OF    ELECTROMOTIVE    FORCE 


tion  may  exist  in  the  manner  in  which  both  of  these  changes  may 
occur. 

A  wave  of  the  form  shown  in  figure  84  is  called  a  sinusoidal 


FIG.  83. — GRAPHIC  REPRESENTATION  OF  A  DISSYMMETRIC  ELECTROMOTIVE  FORCE. 

wave,  and  an  electromotive  force  alternating  in  this  manner  is  called 
a  sinusoidal  electromotive  force. 

The  electromotive  forces  produced  by  friction  are  much  higher 
than  those  produced  by  voltaic  cells  or  dynamo-electric  machines. 
The  electromotive  force  produced  by  a  properly  operated  friction 


FIG.  84.— GRAPHIC  REPRESENTATION  OF  A  SINUSOIDAL  ELECTROMOTIVE  FORCE. 

machine  is  of  the  pulsatory  character.  When  a  pulsatory  electro- 
motive force  attains  a  strength  sufficient  to  discharge  itself  through 
an  air  gap,  it  suddenly  falls  to  a  minimum.  It  then  recovers  and 
again  discharges,  and  this  action  is  carried  on  in  a  pulsatory  manner 


CURRENTS  OF  HIGH  FREQUENCY 


at  frequent  intervals.     Such  a  pulsatory  electromotive  force  is  shown 
in  figure  85. 

Currents  of  High  Frequency. 

Some  consideration  must  be  given  to  a  manifestation  of  the  electric 
energy  that  has  occupied  the  attention  of  students  during  the  last 
years,  and  whose  introduction  into  electrotherapeutics  has  greatly 
enlarged  the  scope  of  this  branch  of  medicine.  We  refer  to  cur- 
rents of  high  frequency.  As  all  electric  sources  produce  electro- 
motive forces,  so  do  all  electromotive  forces  under  suitable  condi- 
tions produce  currents  or  discharges.  The  character  of  the  current 


160 

14(3  • 
120 

<n  100- 

i- 

^     60- 

40- 

20' 

0 


SECONDS 

FIG.  85. — GRAPHIC  REPRESENTATION  OF  A  PULSATORY  ELECTROMOTIVE  FORCE. 

or  discharge  is  dependent  upon  the  character  of 'the  electromotive 
force  that  produces  it,  so  that  no  matter  how  a  discharge  may  differ 
in  appearance  from  some  other  discharge,  this  difference  is  entirely 
dependent  upon  the  character — /.  e.,  the  frequency,  the  magnitude, 
and  the  wave  type — of  its  electromotive  force. 

When  a  ball  prime  conductor  of  a  static  machine  is  made  to 
discharge  the  electricity  with  which  it  has  been  charged,  it  does  so 
in  a  disruptive  manner  or  as  a  spark.  This  seems  to  consist  of  a 
number  of  separate  discharges,  to  and  fro,  between  the  ball  and  the 
object  into  which  it  discharges.  The  discharge  is  an  oscillatory 
one.  When  a  condenser,  as  a  ball  prime  conductor,  charged 
to  a  very  high  potential,  is  discharged  into  a  conductor  having 
8 


114  VARIETIES   OF    ELECTROMOTIVE    FORCE 

a  certain  self-induction  and  slight  resistance,  extremely  rapid, 
isochronous  oscillations  are  produced,  that  constitute  a 
high  frequency  current. 

The  frequency  of  oscillations  is  often  exceedingly  high, 
reaching  at  times  hundreds  of  millions  of  cycles  in  a  second 
(experiments  of  Herz).  The  total  number  of  oscillations  in  one 
discharge  is,  however,  not  very  great.  When  we  consider  that 
the  greatest  number  of  vibrations  that  can  be  appreciated  in  the 
production  of  sound  is  36,000  in  a  second,  we  must  admit  that 
the  term  "  high  frequency,"  as  applied  to  the  electric  oscillations, 
is  well  merited. 

The  following  mechanical  effects  will  clearly  explain  the  phenom- 
enon. If  a  vibrating  straight  spring  be  firmly  fixed  at  one  end,  and 
the  free  end  be  moved  from  its  vertical  position  of  equilibrium  and 
then  again  liberated,  the  spring  will  oscillate  for  a  certain  period  of 
time  before  it  regains  its  former  position  of  equilibrium,  providing- 
that  the  surrounding  medium  is  one  of  slight  resistance,  such  as  air, 
alcohol,  or  water.  If,  on  the  other  hand,  this  medium  be  a  liquid 
of  very  great  density,  as  oil,  there  will  be  no  oscillation,  but  an 
aperiodic  return  to  the  vertical  position. 

Again,  if  in  a  U-tube  partially  filled  with  fluid  a  change  of  level 
be  produced  by  pressure  upon  one  limb,  and  this  pressure  be  sud- 
denly removed,  the  fluid  will  at  once  move  in  both  branches  in  order 
to  re-establish  an  equilibrium,  and  if  the  resistance  to  its  rise  and  fall 
be  slight,  it  will  oscillate  for  a  certain  time  before  coming  to  rest 
at  the  same  level  in  the  two  limbs  ;  if,  on  the  other  hand,  there  be 
a  marked  resistance  to  this  movement  of  fluid,  the  level  will  become 
rerestablished  in  an  aperiodic  manner.  (See  Figs.  86  and  87.) 

In  both  of  these  examples  we  have  slow  cycles  of  visible  move- 
ment. In  both  we  have  a  dissipation  of  energy,  manifesting  itself  in 
the  form  of  heat,  equal  to  the  work  necessary  for  the  production  of 
the  primary  deflection  from  the  position  of  rest. 

In  the  currents  of  high  frequency  we  have,  as  stated,  rapid  cycles, 
with  invisible  movement  and  a  dissipation  of  energy,  in  the  form 
of  emitted  radiations,  whose  existence  can  be  proved  by  the  aid 
of  a  mobile  conductor  passed  in  the  neighborhood  of  the  circuit 
of  high  frequency.  As  the  frequency  of  oscillation  of  the  spring 


OSCILLATORY    DISCHARGES  115 

will  depend  upon  the  elasticity  of  the  spring,  upon  the  strength  of 
fixation,  and  upon  the  resistance  of  the  surrounding  medium,  so  an 
electric  circuit  in  which  a  discharge  suddenly  takes  place  will  follow 
precisely  parallel  laws.  The  resistance  of  the  medium  corresponds 
to  the  resistance  of  the  electric  circuit  in  ohms.  The  elasticity  of 
the  spring  corresponds  to  the  electrostatic  capacity  of  the  circuit  or 
to  its  capacity  as  a  condenser,  and  the  fixation  of  the  spring  corres- 
ponds to  the  inductance  of  the  circuit. 

Therefore  when  a  discharge  is  effected  into  an  electric  circuit, 
this  discharge  will  be  oscillatory  or  nonoscillatory,  in  accordance 


FIG.  86. 


FIG.  87. 


FIGS.  86  AND  87. — SHOWING  THE  OSCILLATIONS  OF  A  LIQUID  IN  THE  LIMBS  OF  A 

U-TUBE. 

with  the  degree  of  resistance  of  the  circuit  as  compared  with  its 
capacity  and  inductance,  and  the  oscillations  will  be  more  powerful 
the  higher  the  electromotive  force  employed  to  produce  the  waves. 
Thus,  the  high  electromotive  force  obtained  from  an  influence 
machine  will  give  very  powerful  oscillations. 

In  electrotherapeutics  W.  J.  Morton,  of  New  York,  many  years 
ago  introduced  the  use  of  such  discharges  under  the  misleading 
name  of  "  static  induced  currents."  These  electric  phenomena  have 
been  well  known  for  many  years,  and  so  far  back  as  1855  Sir 
William  Thompson  gave  the  theory  of  their  causation.  Neverthe- 


u6 


VARIETIES    OF    ELECTROMOTIVE    FORCE 


less,  it  was  not  until  Herz  began  his  series  of  remarkable  experi- 
ments that  the  electric  oscillations  became  the  object  of  great  inter- 
est. Herz  showed  that  these  oscillations  could  be  maintained  by 
means  of  an  induction  coil,  and  that  their  electric  effects  were 
propagated  to  a  distance  in  the  same  manner  as  light.  One  of  the 
arrangements  by  which  Herz  made  his  studies  is  shown  schemati- 
cally in  figure  88. 

I  is  an  induction  coil ;  C  and  D  are  two  balls  1 5  centimeters  in 
diameter,  serving  as  condensers,  and  attached  to  two  small  balls, 
A,  B,  acting  as  dischargers,  by  two  cylindric  rods,  each  5  millimeters 
in  diameter  and  I  ^  meters  in  length.  The  spark  produced  between 


FIG.  88.- 


-ScHEME  OF  HERZ'S  INDUCTION  COIL  FOR   PRODUCING  HIGH  FREQUENCY 
OSCILLATIONS. 


A  and  B  was  one  of  about  1 5  millimeters.  On  account  of  the 
smallness  of  condenser  capacity  and  of  conductors,  the  frequency 
of  oscillations  obtained  reached  100,000,000  in  a  second. 

Tesla  later  made  use  of  two  procedures  in  order  to  produce  the 
high  frequency  currents.  In  the  first  method  he  made  use  of  alter- 
nators with  very  many  poles,  and  by  means  of  transformers  raised 
the  potential  to  tens  of  thousands  of  volts  ;  in  a  second  method  he 
used  a  modified  Herz  apparatus. 

Elihu  Thomson  has  since  then  considerably  modified  and  in- 
creased the  efficiency  of  the  necessary  apparatus. 


PART   II 

APPARATUS   REQUIRED   FOR 

THE  THERAPEUTIC  AND   DIAGNOSTIC   USE 

OF  ELECTRICITY 


PART  II 

APPARATUS  REQUIRED  FOR 

THE  THERAPEUTIC  AND  DIAGNOSTIC  USE 

OF  ELECTRICITY 

ITS  SELECTION    MODE  OF  APPLICATION    AND  CARE 

PRELIMINARY 

The  electric  apparatus  used  in  medicine  are,  as  may  be  deduced 
from  the  preceding  chapters,  of  four  different  kinds  : 

1.  Instruments  supplying  static  electricity; 

2.  Instruments  supplying  dynamic  electricity  ; 

3.  Instruments  supplying  induced  electricity; 

4.  Instruments  that  change  the    character  of    the   electro- 
motive force  derived  from  one  of  the  foregoing. 

The  number  of  apparatus  employed  for  these  varied  purposes  is 
so  great  that  it  is  impossible  to  describe  them  all.  Such  description, 
moreover,  is  unnecessary,  inasmuch  as  the  principles  governing  the 
construction  of  each  class  are  the  same  throughout.  These  prin- 
ciples have  been  sufficiently  elucidated  to  enable  us  to  select  single 
pieces  of  apparatus  as  examples  of  each  class,  and  to  make  their  de- 
scriptions comparatively  brief.  We  must  also  consider  apparatus 
rendering  the  physical  effects  of  the  electric  current  available 
for  treatment  and  diagnosis.  Hereunder  we  include  electrocautery, 
electric  light,  and  the  Rontgen  rays. 


119 


CHAPTER  I 

FRICTIONAL    ELECTRIC    APPARATUS    AND    ITS 

USE 

Influence  Machine.  Charge  and  Recharge.  Care  of  the  Machine.  Attach- 
ments. Insulator.  Electrodes.  Leyden  Jars.  Chains.  Methods  of 
Application.  Indirect  Spark.  Direct  Spark.  Static  Shock.  Static  In- 
sulation. Static  Breeze.  Static  Induced  Current.  Determination  of 
Polarity. 

For  the  medical  use  of  static  electricity  any  good  influence 
machine,  the  type  of  which  is  represented  by  the  Holtz  machine, 
will  suffice  ;  yet  in  order  to  obtain  the  best  results  from  a  machine, 
attention  must  be  paid  to  its  construction,  to  the  size  and  number 
of  its  plates,  to  the  method  of  driving  it,  and  to  its  proper  care. 

In  the  best  modern  machines  all  the  mechanical  features  of  the 
Holtz  machine  have  been  practically  preserved.  The  revolving 
and  stationary  plates  have  been  increased  in  size  and  number, 
to  augment  the  quantity  of  electricity  generated.  This  increase, 
however,  has  its  limit,  and  the  prevalent  opinion  among  the  ex- 
perienced is  that,  for  practical  purposes,  the  best  effects  may  be 
obtained  from  a  machine  having  eight  plates, — four  revolving  and 
four  stationary, — each  of  which  has  a  diameter  of  from  sixty  to  sev- 
enty centimeters.  The  stationary  plates  need  not  be  circular,  but 
may  be  made  of  two  pieces,  to  allow  of  windows  without  necessi- 
tating any  cutting  in  the  body  of  the  glass. 

To  protect  it  against  dust  and  atmospheric  changes,  the  machine 
should  be  incased  ;  and,  for  the  same  reason,  the  seams  and  joints 
of  the  case  should  be  perfectly  tight.  A  machine  may  be  driven 
by  hand  or  by  means  of  a  suitable  motor  (hot  air,  water,  or  electric). 
Hot-air  engines  for  this  purpose  are  expensive,  troublesome,  and 
noisy.  Water  motors  may  satisfactorily  be  employed,  provided 
a  sufficient  water  pressure  be  close  at  hand.  The  transmission  of 
such  force  from  a  distance,  by  means  of  long  belting,  is  unsatis- 
factory. When  a  proper  electric  source,  such  as  a  central  lighting 

120 


INFLUENCE    MACHINES 


121 


FlG.  89. — HOLTZ-TOEPPLER  MACHINE, — (Hirschmanh,  Berlin.') 


122 


FRICTIONAL    ELECTRIC    APPARATUS    AND    ITS    USE 


station,  is  available,  preference  should  be  given  to  an  electromotor. 
The  speed  of  such  motors  is  best  regulated  by  a  properly  con- 
structed rheostat.  Accumulators  may  be  utilized  for  running  the 
motor,  provided  that  they  can  be  charged  from  a  central  station. 


Batteries  for  this  purpose  are  too  troublesome  and  too  expensive. 
The  machines  made  upon  the  Holtz-Toeppler  principles  that  have 
seemed  to  me  to  be  the  most  efficient  are  the  foreign  machines  (one 
made  by  Hirschmann,  of  Berlin,  is  shown  in  figure  89),  and  the 


CYLINDER    MACHINE 


123 


one  that  I  have  made  use  of  for  several  years,  made  by  Waite  & 
Bartlett,  of  New  York,  shown  in  figure  90.  It  is  almost  unneces- 
sary to  say  that  other  manufacturers  make  machines  in  every  way 
equal  to  those  just  mentioned,  and  I  select  these  merely  because 
I  am  most  familiar  with  them. 

A  machine    constructed  \ipon  entirely    different  principles  and 


FIG.  91. — GLAESER'S  CYLINDER  MACHINE. — (Vienna.) 

presenting  certain  advantages  is  made  by  Glaeser,  of  Vienna.  This 
is  a  cylindermachine,and  consists  of  two  hollow  drums  of  hard 
rubber,  one  somewhat  smaller  than  the  other.  The  smaller  drum  is 
air-tight,  and  is  placed  in  the  interior  of  the  larger  one.  Both  are  made 
to  revolve  about  a  common  axle,  but  in  opposite  directions.  The 
machine  is  shown  in  figure  91  and  requires  no  further  explanation. 


124  FRICTIONAL    ELECTRIC    APPARATUS    AND    ITS    USE 

Its  advantages  consist  in  the  durability  and  strength  of  material 
of  the  electric  exciters,  their  form,  and  their  air-tight  construction. 
Hereby  the  machine  may  be  made  to  functionate  in  all  kinds  of 
weather  and  under  any  atmospheric  conditions.  It  gives  larger 
quantities  of  electricity  in  comparison  to  the  rotary  force  employed  ; 
like  an  electrophorus,  it  retains  its  charge  for  a  long  time  ;  and  it 
allows  rotation  in  either  direction  without  loss  of  charge. 

The  disadvantages  are  that  the  machine,  not  being  self-charging, 
must  be  charged  anew  each  time,  and  must,  therefore,  be  made 
easily  accessible,  and  not  be  inclosed  in  a  glass  case. 

Loss  of  Charge  and  Recharging  the  Machine. 

Loss  of  Charge. — The  best  machine  may  lose  its  charge,  whether 
through  having  its  plates  turned  in  the  wrong  direction,  through  the 
entrance  of  moisture  into  the  case  and  its  deposition  upon  the  plates, 
or  through  grounding  both  poles  by  leaving  the  chains  hanging 
from  them  to  the  floor. 

The  plates  may  have  become  loosened  from  the  axle  and,  in 
consequence,  some  may  fail  to  revolve  properly.  The  combs  may 
have  become  displaced  so  as  to  touch  the  glass  or  to  bear  an 
improper  relation  to  the  paper  collectors. 

The  majority  of  American  machines  of  the  Holtz  type  made  for 
therapeutic  purposes  are  now  supplied  with  a  small  Wimshurst,  for 
the  purpose  of  exciting  action  in  the  Holtz  when  it  loses  its  charge; 
and  the  latest  machines  of  this  kind  have  a  small  Wimshurst  included 
in  the  case,  and  so  arranged  that  its  plates  can  be  made  to  revolve 
at  will,  when  the  large  machine  is  in  action,  and  a  charge  be  trans- 
ferred to  the  plates  of  the  latter.  If  the  machine  be  not  so  supplied, 
it  must  be  furnished  with  catskin  rubbers,  which  bear  upon  the  outer 
revolving  plates,  above  the  metal  combs,  and  can  mechanically  be 
stretched  over  the  face  of  the  plate.  To  charge  a  machine  by  such 
catskin  chargers  both  the  machine  and  the  chargers  should  be 
thoroughly  dried.  This  may  be  done  by  exposure  to  the  sun  or 
by  placing  fresh  calcium  chlorid  within  the  case,  or  by  lighting  a 
fire  in  the  room,  or,  under  exceptional  circumstances,  by  all  three 
methods  combined.  After  the  plates  are  thoroughly  dry,  one  starts 
them  by  turning  the  driving  wheel  from  left  to  right  (facing  the 


ATTACHMENTS    FOR    THE    MACHINE  125 

machine).  The  chargers  are  applied  lightly  near  the  edge  of  the 
revolving  plates  for  a  second  or  two,  and  then  swept  across  their 
faces  every  now  and  then  until  the  machine  starts.  The  poles  should 
be  approximated  to  within  two  centimeters,  and  no  chains  should 
be  on  the  poles.  If,  notwithstanding  this,  the  machine  fails  to 
work,  a  piece  of  catskin  is  warmed  over  a  gas-jet,  the  machine  is 
set  in  motion,  and  the  warm  catskin  applied  as  a  rubber  to  the  outer 
plate  as  close  as  possible  above  the  metal  combs. 

Care  of  the  Machine. — To  be  able  to  obtain  the  best  effects 
from  any  machine,  it  should  receive  a  certain  amount  of  care.  It 
should  be  kept  in  a  well-lighted,  dry  room.  The  accumulation  of 
moisture  and  dust  upon  the  poles  or  electrodes  is  one  of  the  most 
serious  obstacles  to  the  successful  working  of  a  machine  ;  hence 
all  its  metallic  parts  should  be  rubbed  each  morning  with  silk  or 
chamois  skin.  All  bearings  and  the  axle  should  be  kept  well  oiled, 
and  the  belt  of  the  machine  should  be  tightened  occasionally. 

It  is  well  also  to  have  fresh  calcium  chlorid  in  the  case  con- 
stantly, so  as  to  keep  the  air  of  the  interior  dry.  In  winter  this  is 
not  always  necessary,  but  in  summer  it  is  absolutely  essential.  The 
calcium  chlorid  is  best  distributed  among  several  dishes,  each  of 
which  may  hold  500  grams  or  more.  So  soon  as  water  accumulates 
on  the  calcium  it  should  be  poured  off,  or  the  salt  may  be  rebaked  in 
a  slow  oven,  the  heat  of  which  must  not  be  great  enough  to  boil  it. 

Attachments  for  the  Machine. — The  attachments  for  the 
machine  consist  of: 

1 .  An  insulated  platformor  some  other  means  of  insulating 
the  patient.      Insulated  platforms  are  cumbrous,  and  take  up  con- 
siderable room.     If  employed,  it  will  be  found  convenient  to  have 
them  so  arranged  that  they  can  be  pushed  under  the  machine  when 
not  in  use.     Much  handier  is  a  rubber  or  glass  plate  upon 
which  any  chair  may  be  placed. 

2.  Asetofelectrodes,  consisting  of  a  large  and  a  small  brass 
ball,  a  metal  point,  a  wooden  point,  a  metal  roller,  an  umbrella  elec- 
trode, a  pistol  electrode,  sponge-covered  electrodes,  and  a  ring  to 
hold  the  chain  away  from  the  patient.     These  electrodes  and  chain- 
holder,  as  furnished  by  Waite  &  Bartlett,  are  shown  in  figure  92. 

3.  A  set  of  brass  chains  of  varying  lengths;  hooks  for  the 


126 


FRICTIONAL    ELECTRIC    APPARATUS    AND    ITS    USE 


attachment  of  the  chains;  Leydenjars  of  different  sizes,  and  a 
brass  rod  for  connecting  the  outer  coverings  of  the  Leyden  jars 
when  they  are  in  use. 


FIG.  92. — ELECTRODES  AND  ACCESSORIES  FOR  STATIC  MACHINE. — ( Waite  6->  Bart- 

lett,  New  York.) 

Methods  of  Application  of  Static  Electricity. 

The  methods  of  applying  the  static  current  are  the  following : 
i.   By  the  indirect  spark. 


THE    INDIRECT    SPARK  I2/ 

2.  By  the  direct  spark. 

3.  By  the  Leyden  jar  spark  or  static  shock. 

4.  By  static  insulation. 

5.  By  the  static  breeze. 

6.  By  the  static  induced  current. 

The  indirect  spark  is  applied  by  placing  the  patient  first  upon 
the  insulated  platform  (Fig.  93) ;  he  is  then  connected  with  the 
machine  by  means  of  a  chain  which  is  hooked  over  one  of  the  poles, 
either  positive  or  negative  ;  the  other  end  being  attached  to  the  chair 
upon  which  the  patient  sits.  A  chain  is  then  attached  to  the  other 
pole  of  the  machine  and  is  grounded.  Grounding  is  best  done  by 
attaching  the  free  end  of  the  chain  to  a  gas  fixture  or  water-pipe ; 
when  this  is  not  possible,  it  may  be  dropped  upon  the  bare  floor. 

The  poles  of  the  machine  are  now  widely  separated,  and  the 
wheels  put  into  rapid  motion.  It  will  be  noticed  at  once  that  the 
hair  of  the  subject  rises  up,  and  if  the  room  be  dark,  a  purplish  light 
will  be  observed  to  escape  from  his  body.  This  condition  is  called 
static  insulation,  and  the  patient  may  thus  be  charged  from  the 
positive  or  negative  pole,  according  to  the  connection.  Finally, 
the  part  of  the  body  to  be  specially  acted  upon  is  approached  by  a 
brass  ball  electrode.  This  electrode  is  attached  to  a  gas-  or  water- 
pipe  by  means  of  a  brass  chain.  The  brass  chain  must  be  passed 
through  a  ring  attached  to  an  insulating  handle,  so  that  it  may  be 
kept  away  from  the  patient's  body.  When  the  ball  comes  to  within 
a  certain  distance  from  the  patient,  a  discharge  of  accumulated 
electricity  occurs  in  the  form  of  a  spark  ;  this  is  known  as  the 
indirect  spark,  because  the  electricity  takes  an  indirect  course 
(through  the  earth)  to  form  a  circuit. 

The  length  of  the  spark  is  directly  proportional  to  the  gen- 
erating power  of  the  machine.  The  volume  of  the  spark  is 
modified  by  the  size  of  the  brass  ball  and  of  the  electrode.  A  large 
ball  will  produce  a  heavier  spark  than  will  a  small  one.  By  using 
a  wooden  ball  instead  of  a  brass  one  numerous  very  fine  sparks 
are  simultaneously  obtained. 

The  removal  of  the  clothing  is  unnecessary.  The  patient  may 
stand  upon  the  platform  if  this  be  preferable  to  sitting. 

The  Direct  Spark. — Here  the  patient  is  attached  in  the  same 


128  FRICTIONAL    ELECTRIC    APPARATUS    AND    ITS    USE 


FIG.  93. — METHOD  OF  APPLYING  THE  INDIRECT  SPARK. 


THE    DIRECT    SPARK  129 

manner  to  one  pole  of  the  machine,  while  the  electrode  is  directly 
attached  to  the  other  pole  by  means  of  a  chain.  The  ring  and  the 
ball  electrode  are  employed,  as  in  the  former  method.  The  length 
of  the  spark  to  be  administered  is  regulated  by  the  extent  of  sepa- 
ration of  the  poles  of  the  machine  and  the  speed  of  revolution  of 
the  plates.  The  further  apart  the  poles,  and  the  more  rapid  the 


FIG.  94. — METHOD  OF  APPLYING  THE  DIRECT  SPARK. 

revolution  of  the  plates,  the  longer  and  the  more  severe  is  the 
spark.     (See  Fig.  94.) 

Leyden  Jar  Spark  (Fig.  95). — In  this  method  a  pair  of  Leyden 
jars  are  first  attached  to  the  poles  ;  their  outer  coverings  of  tin- 
foil are  then  connected  by  means  of  a  brass  rod.  The  poles  are 
then  brought  into  close  approximation,  and  the  electrode  and  the 
chain  leading  to  the  patient  are  arranged  as  in  the  preceding  method. 
9 


130 


FRICTIONAL    ELECTRIC    APPARATUS    AND    ITS    USE 


The  strength  of  the  shock  is  proportional  to  the  separation  of  the 
poles  and  the  size  of  the  jars.  It  is,  therefore,  advisable  in  using 
this  method  to  approximate  the  poles  as  closely  as  possible,  with- 
out actual  contact,  and  to  use  the  smallest  of  jars.  An  increase 
of  strength  can  be  obtained  by  separating  the  poles  and  putting  on 
larger  jars.  In  this  method  the  application  is  best  made  to  the  bare 
skin.  Its  action  is  very  severe,  and  it  should  be  used  with  extreme 
caution. 

Localization. — In  the  preceding  forms  of  application  it  is  some- 


FIG.  95. — METHOD  OF  APPLYING  THE  LEYDEN  JAR  SPARK. 

times  difficult  to  localize  the  spark  to  special  parts  of  the  body  by 
means  of  the  ordinary  ball  electrode,  for  the  reason  that  the  current 
causing  the  spark  always  seeks  the  line  of  least  resistance.  In  order 
to  localize  the  spark  more  precisely  a  directing  electrode,  as 
Morton's  spark  electrode  (Fig.  96),  will  be  found  of  service. 

A  friction  spark  or  static  massage  may  also  be  conveni- 
ently applied,  according  to  any  of  the  methods  just  described,  by 
means  of  the  roller  electrode  shown  in  figure  97.  Such  an 


THE    STATIC    BREEZE  13! 

electrode,  however,  is  not  essential,  as  a  large  ball  electrode  will 
answer  the  same  purpose. 

Static  insulation  has  already  been  described  in  speaking  of  the 
indirect  spark  (Fig.  93).  The  patient  simply  is  charged  from 
either  pole  for  a  variable  length  of  time.  One  pole  is  attached  to 
the  insulated  platform  upon  which  the  patient  stands  or  sits ;  the 
other  pole  is  grounded  by  a  chain  running  to  the  floor  or  to  gas- 
or  water-pipes.  The  poles  of  the  machine  are  separated  as  widely 
as  possible  before  the  wheels  are  set  in  action. 


FIG.  96. — MORTON'S  SPARK  ELECTRODE. 

The  Static  Breeze. — This  method  consists  in  the  withdrawal 
of  the  static  charge  from  a  patient,  by  means  of  an  electrode  that 
is  made  up  of  one  or  more  points.  The  breeze  may  be  applied 
directly  or  indirectly.  If  indirectly,  the  breeze  electrode  is 
grounded,  as  described  in  the  method  of  the  indirect  spark ;  if 
directly,  one  pole  of  the  machine  is  connected  with  the  insulated 
platform,  the  other  with  the  electrode. 

When  it  is  desirable  to  apply  this  breeze  to  the  head,  a  metal 
cap  studded  with  points  is  hung  over  the  head  of  the  patient  and  is 


FIG.  97. — ROLLER  ELECTRODE. 


grounded.  It  should  not  touch  the  patient's  head  or  hair.  Such 
an  electrode  is  shown  attached  to  the  machine  in  figure  90  (p.  122). 
When  it  is  desired  to  concentrate  the  breeze  upon  any  special  part 
of  the  body  and  to  make  an  application  of  some  duration,  the  con- 
centrator and  stand  shown  in  figure  98  will  be  found  serviceable. 
When  used,  one  pole  of  the  static  machine  must  be  connected 
by  means  of  a  chain  to  the  metal  at  D,  the  other  pole,  by  means 
of  a  chain  also,  to  the  platform  or  patient.  The  point  of  the 


132 


FRICTIONAL    ELECTRIC    APPARATUS    AND    ITS    USE 


concentrator  must  be  brought  near  enough  to  the  patient  for  the 
current  to  bear  on  the  part  to  be  treated. 

The  static  induced  current,  so  called,  and  elaborated  by  W.  J. 
Morton,  of  New  York,  in  nature  resembles  somewhat  the  current 
derived  from  the  fine  wire  coil  of  a  medical  induction  coil,  as  it  is 
an  alternating  and  interrupted  current,  but  its  potential  is 


FIG.  98. — CONCENTRATOR  AND  STAND. 

very  mucn  greater  than  that  of  any  medical  induction  coil  ;  it  is 
in  reality  an  oscillating  current  of  high  frequency,  as  has  already 
been  shown. 

To  produce  this  modification  of  current  we  first  hang  a  pair  of 
Leyden  jars  upon  the  arms  of  the  machine.  Chains,  or  better  still, 
insulated  wires,  should  then  be  attached  to  the  outer  coverings  of 


THE   STATIC    INDUCED    CURRENT 


133 


the  jars  (see  Fig.  99),  and  to  the  other  end  of  each  of  these  wires  is 
attached  an  electrode  for  use  upon  the  body  of  the  patient.     These 


FIG.  99. — METHOD  OF  PRODUCING  THE  STATIC  INDUCED  CURRENT. 

electrodes  are   best  covered  with  sponge  and  should  have  long 
insulated  handles. 

The  poles  of  the  machine  should  be  brought  into  contact  before 
the  plates  are  made  to  revolve.     This  is  very  important,  because 


FIG.  loo. — MORTON'S  PISTOL  ELECTRODE. 


the  current  becomes  much  intensified  by  a  separation  of  the  poles. 
No  insulation  of  the  patient  is  necessary  in  this  method.  The 
strength  of  the  current  is  determined  by  the  size  of  the  Ley  den 


134  FRICTIONAL    ELECTRIC    APPARATUS    AND    ITS    USE 

jars  and  by  the  extent  of  separation  of  the  poles.     It  can,  therefore, 
be  varied  at  will. 

Morton,  by  means  of  a  special  electrode,  avoids  the  inconveni- 
ence entailed  by  constantly  separating  and  approximating  the  poles 
of  the  machine.  The  spark  is  thus  not  abolished  entirely,  but  is 
arranged  to  occur  at  a  distance  from  the  patient,  and,  of  course, 
forms  part  of  the  circuit  in  which  he  is  included.  This  electrode  is 
shown  in  figure  100 ;  the  spark  occurs  between  the  two  balls,  which 
may  be  separated  or  approximated  by  means  of  a  trigger.  The 
applications  of  this  handle  are  manifest,  and  when  connected  with 
a  suitable  electrode,  the  spark  may  be  applied,  if  so  desired,  to 
any  accessible  body- cavity. 

Characteristics  of  the  Franklinic  Current. 

The  electricity  yielded  by  static  machines  is  of  very  high 
electromotive  force.  The  number  of  volts  can  be  estimated 
approximately  according  to  the  length  of  the  spark.  The  follow- 
ing table  shows  the  figures  of  Mascart  for  recognition  of  the 
voltage  of  current  according  to  the  length  of  the  spark : 

VOLTAGE  OF  FRANKLINIC  CURRENT. 

Length  of  Tension  in  Length  of  Tension  in 

Spark.  Volts.  Spark.  Volts. 

o.i  cm 5>49°              6.0  cm 101,400 

0.5    " 26,730               7.0    " 107,700 

i.o  " 48,600              8.0   " 112,500 

1.5    " 57,000              9.0   " 115,800 

2.0   " 64,800            10.0  " 119,100 

3.O     " 76,800  I2.O     " I24,2OO 

4.0  " 77,300     15.0  " 127,800 

5.0  " 94,800 

The  amperage  of  the  current,  however,  is  exceedingly  small, 
and  the  chemical  effect,  for  all  practical  purposes,  is  nil. 

Polarity. 

It  is  sometimes  desirable,  when  using  a  static  machine,  to  know 
which  prime  conductor  is  at  a  positive,  and  which  at  a  nega- 
tive, potential.  The  poles  of  the  machine  may  be  best  differ- 
entiated by  observing  a  machine  while  in  action  in  the  dark,  with 
the  external  poles  connected.  The  positive  side  can  then  be 


RECOGNITION    OF    POLARITY  135 

recognized  by  the  fact  that  the  tips  of  the  collecting  comb  show 
points  of  light,  while  upon  the  negative  side  the  light 
appears  in  a  brush-like  form. 

In  the  light,  the  poles  may  be  differentiated  by  the  form  and 
color  of  the  spark  that  passes  between  the  external  conductors 
of  the  machine.  If,  thus,  the  balls  of  the  conductors  be  separated 
to  within  two  centimeters  of  each  other,  the  spark  stream  that 
passes  between  them  shows  a  distinct  violet  portion,  which  begins 
at  the  ball  by  a  bright  point;  this  violet  part  of  the  stream  in- 
dicates the  negative  pole,  while  the  positive  pole  is  char- 
acterized by  a  bright  area  of  white  light  lying  near  it.  If  a 
burning  candle  be  placed  between  the  poles  of  a  machine  in  action, 
the  flame  will  be  diverted  toward  the  positive  pole. 

Since  machines  that  have  not  been  in  use  for  some  time  do  not 
always  charge  themselves  in  the  same  direction,  it  is  necessary  to 
determine  the  polarity  by  one  of  the  foregoing  methods. 


CHAPTER  II 
GALVANIC  APPARATUS  AND   ITS  USE 

Source.  Batteries.  Dynamos.  Regulators.  Selectors.  Rheostats.  Volt 
Controllers.  Arrangement  of  Resistance  in  Circuit.  Reversers.  Inter- 
rupters. Combiners.  Measurement.  Milliamperemeters.  Voltmeters. 
Electrodes.  Cords. 

Galvanic  Apparatus. 

For  the  application  of  galvanic  or  dynamic  electricity  in  its 
various  modifications  for  medical  purposes  we  require,  first,  a  proper 
source  of  electricity — batteries  or  dynamos;  secondly,  some 
arrangement  by  which  the  electromotive  force  and  amperage  of  the 
current  can  be  regulated  or  modified ;  and  in  addition  to  these  a 
means  for  reversing  the  poles,  a  means  for  measuring  both  the 
electromotive  force  and  the  current  strength,  and  a  means  for  lead- 
ing the  current  to  the  body  of  the  patient. 

As  many  of  these  appurtenances  are  essential  for  the  application 
of  all  forms  of  current,  no  matter  what  their  source, — constant, 
magneto-  or  volta  induced,  sinusoidal,  and  high  frequency, — it  will 
be  more  convenient,  in  order  to  avoid  repetition,  to  begin  by  des- 
cribing the  accessory  apparatus,  and  then  to  give  a  description 
of  the  medical  apparatus  itself,  as  employed  for  the  generation  or 
application  of  the  different  currents. 

Means  by  which  the  Current  may  be  Regulated. 

Cell  Selectors. — Rheostats. — Volt  Controllers. — The  most 
important  factor  in  the  use  of  dynamic  electricity,  regardless  of  the 
source  from  which  it  is  derived  or  of  the  manner  in  which  the  char- 
acter of  its  electromotive  force  may  be  modified  for  special  pur- 
poses, is  its  control. 

We  know  that  the  strength  of  a  current — its  amperage — may 
be  increased  or  decreased  by  an  increase  or  decrease  of  electro- 
motive force,  or  by  decreasing  or  increasing  the  resistance 

136 


CELL   SELECTORS  137 

through  which  the  current  flows.     This  increase  or  decrease  of  the 
current  practically  means  its  control. 

As  the  resistance  of  the  external  circuit  (human  body)  is  in  all 
electrodiagnostic  and  electrotherapeutic  applications  very  large,  it 
is  necessary,  when  cells  constitute  the  source  of  current  supply, 
so  to  arrange  these  cells  that  the  pressure  of  the  current  may  easily 
overcome  the  large  external  resistance.  In  order  to  obtain  such 
a  pressure  a  large  number  of  cells  connected  in  series  must  be 
employed.  According  to  Ohm's  law,  the  pressure  of  a  current, 
when  we  are  dealing  with  a  large  external  resistance,  is  almost 
directly  proportional  to  the  number  of  cells  employed.  It  is, 
therefore,  necessary  that  every  battery  that  is  to  be  used  for  electro- 
medical  purposes  should  have  some  arrangement  by  which  the 
pressure  (E  M  F)  and  the  current  strength  may  be  regulated.  This 
may  be  accomplished  by  the  use  of  a  cell  selector. 

Cell  selectors  possess  the  advantage  of  regulating  the  pressure, 
and  with  this  also  the  current  strength,  but  they  present  such 
serious  disadvantages  that  they  have  been  to  a  great  extent  dis- 
placed by  other  apparatus.  Yet  so  many  portable  batteries  made 
by  various  manufacturers  are  supplied  with  this  means  of  current 
regulation  alone  that  a  description  of  their  essential  features  be- 
comes necessary. 

A  good  selector  must  possess  certain  prime  qualities:  (i)  It 
must  admit  of  an  increase  or  a  decrease  of  electromotive 
force,  through  the  introduction  of  one  cell  at  a  time;  (2)  it 
must  permit  of  such  increase  or  decrease  without  producing 
any  interruption  in  the  flow  of  the  current. 

All  selectors  are  constructed  upon  one  of  three  principles  :  the 
crank,  the  rider,  or  the  plug  system. 

The  best  crank  selector  is  the  one  described  by  R.  Remak. 
It  consists  of  a  plate  of  hard  rubber,  upon  which  are  arranged,  in  a 
circle  or  semicircle,  the  metallic  buttons  through  which  the  con- 
nection is  made.  A  metal  crank  pivoting  at  the  center  of  the  circle 
can  be  brought  into  contact  with  each  of  the  buttons  successively, 
thus  allowing  the  current  from  a  greater  or  smaller  number  of  cells 
to  flow  accordingly  through  the  button  upon  which  it  rests.  The 
contact  buttons,  which  are  insulated  from  one  another,  must  still 


138  GALVANIC    APPARATUS    AND    ITS    USE 

be  so  close  to  one  another  that  the  crank  touches  a  button  while 
it  is  covering  the  next  following  one.  By  an  arrangement  in  the 
form  of  two  semicircles — the  first  of  which  selects  one  cell  at  a 
time,  from  i  to  10,  and  the  second  selects  five  cells  at  a  time,  from 
5  to  50 — any  desired  number  of  cells  from  I  to  60  may  be  intro- 
duced singly  ;  yet  only  twenty  contact  buttons  are  used. 

The  plug  selector,  or  Brenner's  selector,  is  so  constructed  that, 
instead  of  buttons  and  a  crank  being  made  use  of,  brass  plates 
and  plugs  are  employed.  Each  metallic  plate  has  a  semicircular 
piece  cut  out  of  each  end,  so  that  when  the  ends  of  two  different 
plates  are  approximated,  but  not  in  contact,  a  circle  is  formed  into 
which  the  metallic  plug  fits  tightly.  When  a  plug  is  introduced  at 
a  certain  hole,  all  the  cells  up  to  the  number  indicated  by  that  hole 
are  thrown  into  the  circuit.  The  withdrawal  of  the  plug  at  once 
breaks  the  current,  and  thus  a  sudden  break  and  make  of  the  cur- 
rent from  any  desired  number  of  cells  may  be  effected.  This  sup- 
posed advantage  is  much  better  attained  by  other  means  (commu- 
tator). 

In  order  to  avoid  such  breaks  of  the  current  in  the  ordinary  use 
of  this  selector  it  is  necessary  to  employ  two  plugs,  one  of  which, 
for  example,  is  put  into  hole  I  and  the  second  into  hole  2 ;  then 
plug  i  is  withdrawn  and  placed  in  hole  3  ;  thus,  by  taking  one 
plug  out  and  putting  it  into  the  hole  immediately  beyond  the  other 
plug,  the  entire  battery  may  be  introduced  cell  by  cell. 

This  cell  selector  is  so  made  by  some  manufacturers  that,  instead 
of  metal  plates  with  holes  for  the  plugs  to  fit  into,  metal  plugs  over 
which  a  split  metal  sheath  fits  tightly  are  employed.  Two  such 
sheaths  are  attached  to  a  bifurcated  conducting  cord,  and  they  are 
placed  over  the  plugs  in  the  same  manner  as  described  for  placing 
the  plugs  in  the  holes. 

The  disadvantages  of  both  of  these  forms  of  selectors  are  so  great 
that  it  is  to  be  hoped  they  will  soon  cease  to  be  a  part  of  instru- 
ments of  American  manufacture,  as  they  have  long  since  ceased  to 
be  found  on  European  apparatus. 

The  rider  form  of  selector  may  fairly  be  represented  by  that  of 
Stoehrer.  It  consists  of  a  rectangular  strip  placed  horizontally 
upon  a  base  ;  along  both  edges  of  the  former  are  fastened,  at  regu- 


RIDER    SELECTORS 


139 


lar  intervals,  plates  of  brass  that  are  connected  with  the  cells  of 
the  battery.  A  metallic  rider  is  placed  over  the  median  portion, 
and  is  movable  between  the  two  rows  of  plates,  and  forms  a  metal- 
lic contact  between  them.  If  the  rider  is  placed  at  o,  no  current 
passes  ;  if  at  the  point  2,  two  cells  are  brought  into  action  ;  thus  the 
further  the  rider  is  removed  from  o,  the  more  cells  are  introduced. 
(See  Fig.  101.) 

For  many  years  a  number  of  physicians  have  made  use  of  a 
selector  that  Dr.  Rudisch  and  I  described  in  1884,  and  that  has 
given  great  satisfaction  to  all  who  have  employed  it.  This  selector 
is  one  that,  although  a  combination  of  all  three  systems,  is  best 
understood  by  describing  it  as  of  the  rider  variety.  It  consists  of 
a  strip  of  hard  rubber  that  is  perforated  by  as  many  metal  plugs  as 


FIG.   101. — RIDER  CELL  SELECTOR. 


there  are  cells  in  the  battery ;  each  plug  ends  in  a  metal  head,  and 
is  connected  below  to  its  corresponding  cell.  Two  strips  of  metal 
run  along  the  sides  of  the  rubber  strip  from  end  to  end  (Fig.  102, 
m  /,  m  2).  The  entire  base  is  surmounted  by  two  riders  that  are 
freely  movable  in  either  direction,  R  i,  R2.  These  riders  consist  of 
a  hard-rubber  body  that  serves  as  a  handle,  to  the  bottom  of  which 
is  attached,  by  means  of  a  strong  spring,  a  metallic  plate  half  as 
large  as  the  head  of  a  plug  (Fig.  103,^,  /).  The  whole  rider  is 
kept  in  place  by  two  side-pieces,  best  described  as  clamps  (Fig.  103, 
e,  c,  e,  c),  and  that  are  in  close  connection  with  the  metallic  strips 
m  i  and  m2,  figure  102  ;  it  is  lined  by  a  thin  plate  of  metal,  so  that 
a  direct  metallic  connection  is  formed  between  the  rider  and  the 
metallic  strips.  This  metal  lining  is  not  continuous,  but  is  broken 


140 


GALVANIC    APPARATUS    AND    ITS    USE 


at  the  upper  clamp  of  the  one  rider,  and  the  lower  clamp  of  the 
other  (Fig.  103,  Bri,  Br  2).  The  selector  is  connected  and 
operated  as  follows : 

The  metallic  strips  are  connected  one  with  each  binding  post 
or  electrode.  The  zinc  of  each  cell  is  connected  seriatim  with  the 
corresponding  plug  of  the  selector.  It  will  thus  be  seen  that, 
the  cells  being  connected  among  themselves  in  series,  all  the  cells 
that  lie  between  the  plugs  upon  which  the  riders  rest  will  be  in  the 
circuit,  while  those  lying  exteriorly  to  the  riders  are  not  in  circuit. 
For  example,  let  the  rider  R  i  be  placed  upon  button  2  and  the 


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FIG.  102. — COMBINED  CELL  SELECTOR. 

rider  R  2  upon  button  9.  The  current  will  pass  from  the  second 
cell  to  the  second  plug,  then  into  the  first  rider,  R  /,  placed  upon 
this  plug ;  then,  because  the  connection  above  is  broken,  it  passes 
to  the  lower  metallic  strip,  and  thence  through  the  connecting  wire 
to  the  binding  post  (Pi,  Fig.  102).  Thence  the  current  passes 
through  the  body  connecting  the  two  posts,  to  the  second  binding 
post,  P 2,  through  the  wire  to  the  upper  metallic  strip,  along  this 
to  rider  R2,  and  thence  into  plug  9,  upon  which  the  latter  rests, 
thus  completing  the  circuit.  The  advantages  of  this  selector, 
which  may  be  variously  modified,  are  that:  (i)  There  is  always 


COMBINED    CELL    SELECTOR 


a  firm  connection  between  the  rider  and  the  plugs.  (2)  The 
cells  can  be  introduced  into  the  current  singly.  (3)  The 
first  cells  of  the  battery  do  not  become  worn  before  the 
others.  Whatever  may  be  the  position  of  the  riders,  the  only 
cells  comprised  in  the  circuit  are  those  situated  between  the 
riders,  and  all  cells  situated  in  front  of  the  one  and  behind  the 


Ri. 


R2. 


Brl, 


Oli 


Br2.' 


FIG.  103. — RIDERS  OF  COMBINED  CELL  SELECTOR. 

other  rider  form  an  isolated  series.  (4)  By  means  of  this  selector 
any  disorder  of  function  in  the  circuit  of  any  cell  may  be 
surely  and  quickly  located  ;  thus,  if  the  riders  are  approximated 
so  that  each  one  covers  the  plug  connected  with  the  adjoining 
cells,  and  they  are  then  moved  together  along  the  selector  base, 
each  cell  is  taken  singly,  and  any  disorder  will  at  once  be  indicated 
by  a  galvanometer  placed  in  the  circuit. 


FIG.  104. — GAIFFE'S  CELL  SELECTOR. 

A  similar  contrivance,  shown  in  figure  104,  has  for  many  years 
been  made  use  of  by  Gaiffe,  of  Paris.  A  circular  form  may  also  be 
given  to  this  selector. 

Regulation  by  Rheostat. — Instead  of  increasing  or  diminishing 
the  current  strength  by  increasing  or  decreasing  the  voltage,  as  is 


142  GALVANIC    APPARATUS    AND    ITS    USE 

done  when  a  selector  is  employed,  the  current  strength  may  be 
regulated  more  practicably  through  the  introduction  of  a  variable 
resistance,  a  rheostat,  into  the  circuit.  We  then  make  use  of 
the  entire  electromotive  force  of  the  source  at  our  command,  or 
of  a  suitable  part  of  it,  and  reduce  the  amperage  by  increasing 
the  resistance  in  the  circuit. 

The  method  of  making  use  of  the  entire  available  current  and 
regulating  its  strength  by  means  of  a  rheostat  has  one  very  grave 
practical  objection,  and  that  is  that  the  intensity  (pressure)  of  the 
entire  source  accompanies  even  the  smallest  amount  of  current 
strength  applied,  and  thus  materially  increases  the  pain  of  the 
application.  This  objection,  however,  can  readily  be  obviated,  for 
there  can  no  longer  be  any  doubt  that  the  increase  of  pain  with 
an  increase  of  the  current  is  dependent  upon  the  manner  in  which 
the  resistance  is  placed  in  the  circuit.  There  certainly  is  a  differ- 
ence between  applying,  say,  ten  milliamperes  of  current  at  a  pres- 
sure of  seventy-five  volts,  through  a  resistance  placed  in  series  with 
the  patient,  and  applying  the  same  number  of  milliamperes  with 
the  resistance  so  placed  that  the  pressure  is  reduced  to  a  degree 
just  sufficient  to  overcome  the  resistance  of  that  part  of  the  body 
which  is  being  treated.  The  accompanying  sketch  illustrates  the 
manner  in  which  this  regulating  resistance  should  be  employed. 
(See  Fig.  105.) 

The  regulation  is  here  effected  by  means  of  the  shunt  principle, 
explained  on  page  65,  and  which,  practically  applied,  is  shown  in 
figure  105.  B  is  a  battery  from  which  the  current  flows  from  + 
to  R  (resistance)  ;  a  certain  portion  of  this  current  is  forced  through 
this  resistance  and  passes  to  — ,  thus  completing  the  circuit. 

This  portion  of  current  is  wasted,  and  therefore  it  is  well  to 
make  the  resistance  as  large  as  is  practicable  in  proportion  to  the 
pressure  in  the  main,  thereby  minimizing  the  loss  of  current.  If,  for 
instance,  our  battery  represents  an  electromotive  force  of  40  volts, 
and  we  introduce  into  the  main  circuit  a  resistance  of  10,000  ohms, 
the  current  forced  through  this  resistance  will  be  C  =  E^F  = 
~^,  or  0.004  ampere,  which  amount  represents  the  actual  loss 
of  current.  By  a  shunt  we  now  derive  our  therapeutic  current :  one 


REGULATION  BY  RHEOSTAT 


143 


conductor  is  attached  at  a  point  C,  and  the  other  to  a  bar,  which 
carries  a  slide  contact  C2,  electrically  connected  to  this  bar. 

As  the  flow  of  current  through  a  shunt  is  directly  proportional 
to  the  resistance  in  the  main,  no  current  will  be  obtained  at  T+ 
and  T —  when  the  slide  contact  C2  is  nearest  to  C, —  that  is,  if 
there  be  no  resistance  to  speak  of  between  C2  and  C ;  as  soon, 
however,  as  we  slide  C2  away  from  C,  and  thus  introduce  resis- 
tance, a  current  will  be  obtained  at  T-p->  T — ,  whose  intensity  will 
increase  until  all  the  resistance  has  been  interpolated  between  C 
and  C2. 

The    comparatively   feeble    currents    employed    in   therapeutics 


FIG.  105. — SHOWING  REGULATION  OF  CURRENT  BY  RESISTANCE  IN  SHUNT. 


admit  of  the  use  of  wire,  carbon,  or  water  as  such  resis- 
tance material. 

Wire  rheostats  are  frequently  used,  and  are  the  only  suitable 
ones  for  measuring  purposes,  as  they  are  the  most  accurate  and 
least  subject  to  change.  The  principle  of  their  construction  has 
already  been  described  (see  Measurement  of  Resistance),  and  the 
metal  rheostats  employed  in  medicine  are  all  more  or  less  modified 
resistance  coils  or  boxes. 

Whenever,  as  is  the  case  in  all  therapeutic  work  and  in  nearly  all 
diagnostic  work,  direct  measurement  of  the  interposed  resistance  is 


144 


GALVANIC    APPARATUS    AND    ITS    USE 


not  required,  a  single  wire  coil  may  be  employed.  The  resistance 
of  this  coil  must  then  be  so  great  that  when  the  entire  coil  is  in 
circuit  practically  no  current  can  pass.  Such  a  single  wire  coil  may 
also  be  replaced  by  a  column  of  some  other  material  that  is  of 
much  higher  resistance  than  metal  wire  and  is  much  less  expensive. 
Such  materials  are  graphite  and  liquids. 

Graphite  Rheostats. — Convenient  and  inexpensive  rheostats 
furnishing  a  high  resistance  and  admitting  of  gradual  and  extensive 
variations  of  the  current  may  be  made  of  graphite.  The  simplest 
practical  form  of  such  rheostat  is  that  shown  in  figure  106,  which 
was  constructed  by  Dr.  J.  Rudisch,  of  New  York,  and  which  I 
demonstrated  to  the  American  Neurological  Association  in  1881. 
This  instrument  consists  of  a  plate  of  ground  glass,  G  (Fig.  106), 


FIG.   106. — GRAPHITE  PENCIL  RHEOSTAT. 


upon  which  glides  a  thick  graphite  pencil,  P  ;  as  the  pencil  is  moved 
to  and  fro  over  the  glass,  graphite  is  rubbed  into  the  glass  and  a  path 
furnished  for  the  current  to  flow.  The  current  enters  the  instru- 
ment at  the  binding  post  A,  flows  from  there  to  the  graphite  mark 
on  the  glass,  along  this  mark  to  the  pencil,  up  through  the  pencil 
along  the  metallic  connection  R  to  the  binding  post  B.  It  will  be 
apparent  that  the  less  graphite  there  is  upon  the  glass,  the  greater 
will  be  the  resistance ;  that,  therefore,  the  resistance  may  be  varied 
at  will  by  rubbing  more  graphite  on  the  glass,  and  by  increasing 
or  decreasing  the  distance  between  the  point  of  entrance  of  the  cur- 
rent and  the  graphite  pencil. 

This  rheostat  has  been  modified  by  giving  it  a  circular  form  and 
by  using  a  metal  spring  instead  of  a  pencil  for  contact  with  the 


GRAPHITE    RHEOSTATS 


145 


graphite,  which  then  must  be  supplied  from  some  other  source 
(Fig.  107). 

Pulverized  carbonaceous  material  is  sometimes  substituted  for 
graphite,  alone  or  in  combination  with  some  fixing  substance,  and 
pressed  into  a  groove  in  an  insulating  plate.  Such  a  rheostat  is 


FIG.  107. — MODIFIED  GRAPHITE  RHEOSTAT. 

shown  in  figure  108.  Here  a  revolving  handle  makes  direct  con- 
tact with  a  carbon  column  in  the  groove  beneath.  The  length  of 
the  carbon  column  inserted  between  the  terminals  can  be  varied  by 
turning  the  handle.  The  resistance  is  proportional  to  the  length 
of  the  carbon  column  included  between  the  handle  and  the  starting- 
point. 


FIG.  108. — MODIFIED  GRAPHITE  RHEOSTAT. 

Another  form  of  carbon  rheostat,  one  that  I  have  used  for 
years  and  found  very  satisfactory  when  employed  with  the  battery 
current,  is  the  Vetter  rheostat.  The  fundamental  principle  upon 
which  the  action  of  this  instrument  depends  is  the  effect  of  variation 
in  resistance  that  takes  place  in  a  quantity  of  carbon  subjected  to  a 
change  in  pressure.  Figure  109  shows  the  instrument  complete, 


146 


GALVANIC    APPARATUS    AND    ITS    USE 


and  figure  no  illustrates  its  working  parts.     In  this  instrument  a 
quantity  of  finely  powdered  carbon  is  contained  in  a  small  rubber 


FIG.  109. — VETTER  RHEOSTAT. 


POST.  NY. 

FIG.  no. — WORKING  PARTS  OF  VETTER  RHEOSTAT. 


cylinder  placed  between  two  metal  plates,  the  opposing  ends  of  a 
circuit.  The  lower  plate  is  affixed  to  the  base  of  the  instrument,  and 


FLUID    RHEOSTATS 

the  other,  traveling  on  upright  guides,  can  be  depressed,  by  means 
of  a  screw,  so  as  to  compress  the  carbon  in  the  rubber  cylinder. 
In  its  ordinary  position — that  is,  when  the  rubber  cylinder  is  not 
compressed — the  contained  carbon  is  held  by  the  rubber  tightly 
against  the  poles,  and  in  this  elongated  position  offers  the  greatest 
degree  of  resistance  to  the  current. 

As  the  knob  B  is  turned  "on"  it  forces  the  upper  pole  down 
against  the  carbon,  which,  for  lack  of  space,  bulges  the  rubber 
cylinder  out  at  the  sides,  thus  diminishing  the  quantity  of  carbon 


FIG.  in. — FLUID  RHEOSTAT. 

and  the  distance  between  the  poles  until,  if  required,  "  hard  con- 
tact "  is  made.  The  reverse  order  of  events  takes  place  when  the 
knob  is  turned  "off,"  the  flexible  quality  of  the  rubber  causing  it 
gradually  to  resume  its  former  shape,  and,  by  forcing  the  carbon 
back,  to  keep  it  in  good  contact  with  the  poles.  The  mechanical 
construction,  which  involves  the  principle  of  the  letterpress,  is  almost 
perfect,  and,  electrically  considered,  it  offers  great  advantages. 

Fluid  Rheostat. — Another  form  of  rheostat  much  used  in  medi- 
cine is  the  fluid   rheostat.     The  principle  of  such  an  instru- 


148 


GALVANIC    APPARATUS    AND    ITS    USE 


ment  is  that  a  column  of  water  shall:  be  so  contained  in  a  vessel 
that,  by  means  of  a  pair  of  separate  metal  electrodes,  a  greater  or 
smaller  part  of  the  column  of  water  may  be  interposed  between 
the  terminals  ;  then  the  further  apart  the  terminals  of  these  elec- 
trodes may  be,  the  greater  will  be  the  column  of  water  between 
them,  and  the  greater  the  resistance  opposed  to  the  flow  of  current. 
The  scope  of  such  an  instrument  will  depend  upon  the  length  of 
the  column  of  fluid,  the  diameter  of  the  electrodes,  and  the  con- 
ductivity of  the  fluid.  An  excellent  instrument  of  this  kind  is 
made  by  Hirschmann,  of  Berlin,  and  is  shown  in  figure  1 1 1. 

The  chief  objection  to  the  use  of  such  instruments,  however,  is 
that  the  polarization  that  necessarily  takes  place  in  them  produces 


FIG.  112. — IMPROVED  FLUID  RHEOSTAT. 

a  constant  change  in  their  resistivity.  The  use  of  a  depolarizing 
fluid  is  impracticable ;  as  any  fluid  of  sufficient  depolarizing  power 
would  be  so  good  a  conductor  of  electricity  that  the  rheostat 
containing  such  would  be  unserviceable. 

In  the  form  shown  in  figure  1 1 2  these  difficulties  are  practically 
overcome.  The  electrodes  and  connections  exposed  to  the  fluid 
are  made  of  carbon  and  tin  and  will  not  oxidize,  and  the  water  can 
easily  be  changed  from  time  to  time.  I  consider  this  the  best  form 
of  water  rheostat. 

The  Choice  and  Use  of  Selectors  and  Rheostats. 

If  selectors  are  to  be  used  at  all,  they  should,  in  my  opinion, 
be  employed  only  for  the  regulation  of  the  voltage  of  a  battery 


PRINCIPLES    OF    CURRENT    REGULATION  149 

current,  or  for  purely  scientific  purposes.  In  the  former  case  the 
number  of  volts  that  we  desire  to  work  with  should  be  selected  by 
means  of  the  cell  selector,  and  the  current  given  by  this  voltage 
regulated  by  means  of  a  rheostat.  It  is,  therefore,  better  to  have 
a  small  selector, — one  that  selects  the  cells  in  series  of  five  or  even 
ten, — and  then  to  regulate  the  strength  of  this  current  by  means 
of  a  rheostat.  By  this  means  all  the  advantages  of  volt  control- 
ling may  be  obtained,  while  the  disadvantages  caused  by  compli- 
cated wiring,  and  therefore  by  more  frequent  disorder,  are  obviated. 

For  purely  scientific  purposes  a  selector  that  selects  the  cells 
singly  and  seriatim  is  desirable.  Of  the  choice  of  the  rheostat,  it 
may  be  said  that  metal  rheostats  are  more  accurate.  They  are  the 
best  for  scientific  purposes  and  measurement,  and  when  expense  is 
no  objection,  they  should  always  be  employed. 

In  view  of  the  fact  that  the  selector  is  of  use  only  with  battery 
currents,  it  is  desirable  to  have  some  other  device  for  the  reduction 
of  pressure,  together  with  a  satisfactory  rheostat.  This  combina- 
tion of  volt  controller  and  rheostat  is  undoubtedly  the  most  scien- 
tific, and  practically  the  most  satisfactory,  method  of  regulating  a 
current  for  diagnostic  or  therapeutic  purposes. 

The  mode  of  regulation  of  the  current  by  means  of  a  change 
of  voltage  or  of  pressure  is  apparent  when  we  recall  that  if  in  a 
circuit  the  resistance  remain  constant,  the  current  will  vary  directly 
with  electromotive  force.  For  instance,  if  the  resistance  of  a  wire 
be  two  ohms  and  the  electromotive  force  at  its  terminal  two  volts, 
one  ampere  of  current  will  flow.  If  the  voltage  be  doubled  (four 
volts),  the  current  also  will  be  doubled.  Now,  if  the  current  pass- 
ing through  the  conductor  remain  constant,  we  see  from  the 
formula  E  M  F  =  C  X  R  that  the  electromotive  force  between 
any  two  points  in  the  conductor  will  be  directly  proportional  to  the 
resistance  of  the  conductor  between  these  two  points. 

Let  us  return  to  our  assumed  battery  of  forty  volts  pressure, 
with  a  resistance  of  10,000  ohms  in  the  main  circuit,  and  let  us 
assume,  furthermore,  that  the  resistance  is  made  up  of  the  cylindric 
body,  the  total  or  highest  resistance  of  which  lies  between  its 
terminals  E  and  o  (Fig.  113),  and  that  this  resistance  is  evenly 
distributed  along  the  surface  of  the  cylinder. 


I5O  GALVANIC    APPARATUS    AND    ITS    USE 

Then  a  voltmeter  whose  terminals  are  brought  into  contact  with 
the  surface  of  said  cylinder  will  indicate  an  intensity  of  current  that 
is  in  direct  proportion  to  the  length  of  the  part  of  the  cylinder  that 
lies  between  these  terminals.  Thus,  if  one-fourth  of  the  entire 
cylinder  be  connected  between  the  terminals  of  the  voltmeter,  the 
meter  will  indicate  one-fourth  of  the  initial  voltage.  If,  now,  a 
scale  be  affixed  to  the  resistance  coil, — a  scale  that  has  been  properly 
graded  so  that  each  division  corresponds  to  one  volt, — then  the 
voltage  may  be  read  directly  from  this  scale  without  the  use  of  the 
voltmeter.  But  inasmuch  as  we  are  also  introducing  resistance 
directly  into  the  circuit,  not  only  the  voltage,  but  also  the  current 
itself,  will  thereby  be  reduced.  Herein  we  have,  therefore,  a  reli- 


FIG.  113. — SHOWING  METHOD  OF  REGULATION  OF  CURRENT  BY  PLACING 
RESISTANCE  IN  CIRCUIT. 


able  method  for  simultaneously  reducing  the  voltage  and  the 
amperage  of  a  current.  Such  volt  controllers  are  made  by 
the  Wappler  Electric  Controller  Company,  of  New  York,  and  I 
have  used  them  exclusively  for  two  years  without  discovering  a 
single  defect  in  the  principle  or  in  their  construction. 

The  mechanical  arrangement  of  such  controlling  apparatus  for 
the  battery  current  can  easily  be  deduced  from  the  foregoing  re- 
marks ;  in  describing  the  controllers  for  the  electric-light  current, 
it  will  become  necessary  to  refer  to  them  again. 

A  properly  constructed  water  rheostat  also  presents  many 
advantages,  and  when  used  in  combination  with  the  cell  selector  or 
volt  controller  and  a  battery  current,  leaves  nothing  to  be  desired 


ARRANGEMENT    OF    RHEOSTATS  151 

for  therapeutic  or  diagnostic  purposes.  Especially  can  a  current 
that  is  to  be  applied  with  great  care  and  delicacy,  as  for  instance 
to  the  head,  be  efficiently  regulated  thereby. 

The  carbon  rheostats  also  are  serviceable,  so  far  as  my  experi- 
ence goes,  only  when  used  with  a  battery  current,  and  then,  of 
course,  not  for  scientific  work.  In  the  use  of  the  street  current 
they  are  decidedly  unsatisfactory,  and  are  so  because  their  resistivity 
is  greatly  altered  by  the  heat  produced  by  this  current,  so  that  after 
a  time  they  fail  to  accomplish  the  purpose  for  which  they  were 
designed. 

Rheostats  may  be  connected  in  two  different  ways  :  first, 
in  the  main,  or,  secondly,  in  a  branch  (shunt),  circuit. 


FIG.  114. — SHOWING  A  RHEOSTAT  PLACED  IN  CIRCUIT. 

The  manner  of  connecting  the  rheostat  in  the  main  circuit  is 
shown  in  figure  114.  Here,  of  course,  the  more  resistance, 
R,  that  is  interposed, — that  is,  the  more  rheostat  there  is  in  the 
current, — the  less  current  will  flow  through  the  body,  B. 

If  the  rheostat  be  placed  in  the  branch  circuit, — i.e.,  shunted, 
as  in  figure  1 1 5, — it  will  be  clear,  according  to  the  principles  already 
explained,  that  two  paths  are  open  to  the  current :  the  one  through 
the  main  circuit,  in  which  the  body  is  placed,  the  other  through  the 
branch  circuit.  The  current  always  takes  the  path  of  least 
resistance,  and  as  the  human  body  possesses  high  resistance, 
the  current,  when  the  circuit  is  closed,  will  flow  through  the  shunt, 


152 


GALVANIC    APPARATUS    AND    ITS    USE 


and  little  or  no  current  through  the  body.  If,  now,  a  rheostat,  R,  that 
possesses  a  higher  resistance  than  the  human  body  be  introduced 
into  the  shunt,  the  current  will  flow  through  the  circuit  of  least 
resistance — that  is,  through  the  body,  B.  It  is,  therefore,  evident 
that  the  more  resistance  that  is  introduced  in  the  shunt, 
the  more  current  will  flow  through  the  body. 

For  the  regulation  of  battery  currents  the  rheostat  should 
always  be  placed  in  the  main  circuit.  Such  rheostats  must 
have  a  resistance  of  not  less  than  40,000  ohms,  and  one  whose 


FIG.  115. — SHOWING  A  RHEOSTAT  PLACED  IN  SHUNT. 


resistance  can  be  raised  to  50,000  or  even  100,000  ohms  is 
preferable. 

The  reason  why  a  shunted  rheostat  should  not  be  employed  in 
connection  with  a  battery  current  is  because  a  battery,  to  give 
good  service,  should  have  all  connections  arranged  in  as  simple  a 
manner  as  possible,  and  because  the  cells  are  unnecessarily  used 
when  a  shunt  is  employed.  The  latter  point  is  shown  by  the 
following : 

If,  for  instance,  with  a  current  of  15  Leclanche  cells  2  milli- 
amperes of  current  pass  through  the  body,  the  shunt  rheostat  would 
require  a  resistance  of  85  ohms,  in  which  case  250  milliamperes 
would  flow  through  the  shunt,  so  that  the  battery,  instead  of  furnish- 
ing 2  milliamperes,  would  have  to  furnish  252  milliamperes,  of 


INTERRUPTERS,  REVERSERS,  AND  COMBINERS         153 

which  only  2  are  utilized.     The  following  table  clearly  illustrates 
this  loss  : 

3  ma.  through  body  require    300  ohms  shunt  R  =  100  ma.  through  shunt. 

4  "         "  "          "         325     "         "      "  =    60   "         "  " 

5  "         "  "          "         700     "         "      "  =    30  "         "  " 

6  "         "  "          "       1400     "         "      "  =    15    "         "  " 

It  will  be  seen  that  this  loss  of  current  diminishes  with  the  increase 
of  current  to  be  utilized.  When,  therefore,  we  desire  to  employ 
large  currents,  or  when  the  internal  resistance  of  a  battery  is  high, 
this  objection  loses  much  of  its  force. 

When  we  have  an  unlimited  supply  of  current,  as  in  cur- 
rents from  central  stations,  the  arrangement  of  the  rheostat  in 
the  shunt  is  the  most  practical,  as  such  rheostats  require  a  maxi- 
mum resistance  of  not  more  than  from  3000  to  5000  ohms,  and 
thus  become  simpler  and  cheaper. 

The  method  of  using  the  rheostat  is  as  follows  :  Beginning 
with  the  rheostat  at  zero,  one  selects,  by  means  of  the  cell  selector 
or  volt  controller,  so  much  electromotive  force  as  is  desired  for  the 
individual  case.  He  then  gradually  moves  the  resistance  regulator, 
introducing  resistance  as  slowly  and  regularly  as  possible,  until  the 
galvanometer  needle  indicates  the  figure  representing  the  current 
that  he  desires,  or,  in  electrodiagnosis,  until  a  minimal  contraction 
is  obtained. 

Current  Interrupters,  Reversers,  and  Combiners. 

In  the  application  of  the  dynamic  current  the  necessity  fre- 
quently arises  for  suddenly  breaking  and  then  again  making 
the  current,  or  for  reversing  its  direction.  The  contingency 
is  best  met  by  effecting  the  desired  change  in  the  metallic  part  of 
the  circuit,  without  removing  the  electrodes  from  the  patient. 

The  mechanism  by  which  the  current  can  be  broken  and  made 
at  will  is  known  as  the  current  interrupter ;  that  by  which  the 
current  can  be  changed  and  its  polarity  reversed  is  called  a  current 
reverser  or  commutator.  It  is  most  practical  to  combine  these 
two  mechanisms  in  one,  so  that  by  means  of  a  current  interrupter 
we  can  reverse,  as  well  as  break  and  make,  the  current. 

A  convenient  commutator  is  made  in  the  shape  of  two  springs, 


154 


GALVANIC    APPARATUS    AND    ITS    USE 


joined  transversely  and  movable  over  three  metal  buttons.  The 
mechanism  of  the  instrument  is  shown  in  figure  116.  If  the 
springs  are  in  the  position  indicated  in  the  diagram, — A  resting 
upon  2,  B  upon  3, — then  A  will  be  negative  and  B  positive  ;  if  they 
are  moved  slightly,  so  that  both  A  and  B  rest  between  the  buttons 
in  the  position  A'  and  B',  the  current  will  be  interrupted ;  if  they 


FIG.  116. — COMMUTATOR. 

are  moved  to  the  other  extreme,  so  that  A  rests  upon  I,  B  upon  2, 
A  will  become  positive  and  B  negative,  the  current  being  reversed. 
Current  reversers  are  manufactured  in  many  different  shapes  ;  the 
principle,  however,  is  always  the  same. 

Galvano-faradaic  Combiner. — It  often  becomes  desirable  in 
electrodiagnosis  to  be  able  to  change  rapidly  from  the  gal- 
vanic to  the  faradaic  current,  and  vice  versa,  or  in  electro- 


GALVANO-FARADAIC    COMBINER 


155 


therapeutics  to  make  use  of  these  two  currents  in  combina- 
tion in  the  form  of  a  galvano-faradaic  current. 

De  Watteville  has  devised  an  instrument  by  means  of  which  he 
facilitates  the  interruption  and  reversal  of  the  galvanic  current,  as 
well  as  the  use  of  the  galvanic  and  faradaic  currents  alternately  or 
in  combination — i.  e.,  the  galvano-faradaic  current.  The  apparatus 
is  made  up  of  two  reversers  similar  to  the  one  just  described  in 
figure  1 1 6,  and  its  mode  of  action  and  wiring  is  shown  in  figure 
117.  Two  pairs  of  screws,  G,  F,  receive  connecting  wires  from 
the  poles  of  the  galvanic  and  faradaic  apparatus  respectively. 


FIG.  117. — GALVANO-FARADAIC  COMBINER. 


When  the  springs  rest  upon  I  and  2,  the  galvanic  current  alone 
circulates ;  when  upon  2  and  3,  the  faradaic  ;  when  upon  I  and  3, 
as  in  the  diagram,  the  galvanic  current  passes  through  2  to  F — , 
thence  through  the  coil  to  F-f,  to  3,  and  finally  reaches  ±  or +, 
to  which  the  electrodes  are  attached,  according  to  the  position  of 
the  reverser ;  having  traversed  the  body,  it  completes  its  circuit 
through  the  opposite  half  of  the  apparatus,  G,  and  the  battery.  If 
the  faradaic  current  is  flowing  at  the  same  time,  it  passes  through 
the  same  circuit.  When  all  connections  are  made  as  in  the  diagram, 
the  galvanic  polarity  of  the  electrodes  attached  to  +  and  ±  may 


156  GALVANIC    APPARATUS    AND    ITS    USE 

easily  be  determined  by  remembering  that  the  commutator  ABC 
always  points  to  the  positive  terminal. 

Measurement  of  Current. 

We  have  just  seen  that  the  strength  of  the  galvanic  current  can 
be  regulated  in  a  variety  of  ways,  and  we  also  know  that  the 
strength  of  a  current  at  any  time  can  be  measured  by  means  of 
suitable  instruments.  Formerly  it  was  considered  sufficient  if  the 
measurement  of  the  current  strength  was  determined  by  the  num- 
ber of  cells  made  use  of  or  by  the  angle  of  deflection  of  the  needle 
of  a  galvanoscope.  It  is,  however,  evident  that  such  measurements 
possess  no  value  whatsoever,  as  they  are  only  relative  and  never 
absolute.  Therefore  some  generally  applicable  system  of  measure- 
ment that  would  admit  of  an  intercomparison  of  the  results  obtained 
by  investigators  at  different  places  must  be  employed. 

After  a  number  of  investigators,  more  especially  de  Watteville, 
had  recommended  the  division  of  the  galvanometers  into  units 
(millimeters,  afterward  milliamperes),  Gaiffe  constructed  the 
first  so-called  absolute  horizontal  galvanometer,  and  yet  his  instru- 
ment did  not  answer  all  requirements  satisfactorily.  When,  how- 
ever, Edelmann,  in  1882,  upon  von  Ziemssen's  suggestion,  con- 
structed his  unit  horizontal  galvanometer,  he  therewith  furnished 
all  future  instrument  makers  with  a  basis  for  the  construction  of 
meters  for  medical  work,  and  through  this  instrument  the  question, 
whether  the  currents  employed  in  medicine  can  be  measured  easily 
and  surely,  is  categorically  determined  in  the  affirmative. 

Only  magnetic  measuring  instruments  are  available  for  the  meas- 
urement of  currents  used  in  medicine.  In  discussing  the  principles 
upon  which  these  instruments  depend  we  saw  that  they  all  consist 
of  a  movable  magnet,  and  a  current  surrounding  this  magnet.  We 
differentiate  between  horizontal  and  vertical  galvanometers 
according  to  whether  the  movable  magnet  turns  upon  a  vertical  or 
a  horizontal  axis  ;  in  the  latter  the  movable  magnets  swing  in  a 
horizontal  plane  ;  in  the  former,  in  a  vertical  one. 

Any  milliamperemeter  that  is  to  prove  satisfactory  for  both 
diagnostic  and  therapeutic  use  must  be  constructed  with  the  follow- 
ing desiderata  in  view : 


MEASUREMENT    OF    CURRENT  157 

The  instrument  must  be  of  a  low  resistance.  It  must  not  be 
influenced  by  outside  magnetism,  and  it  must  be  independent  of 
the  action  of  gravitation.  Its  scale  must  be  sufficient  in  extent 
(0—50  milliamperes),  and  the  divisions  should  be  uniformly  distributed 
over  the  entire  scale  and  not  crowded  together  at  its  end.  The 
magnet  should  swing  aperiodically,  and  the  instrument  should  give 
equal  deflection  of  the  indicator  to  both  sides  of  the  scale,  deflections 
to  one  side  indicating  the  flow  of  current  in  one  direction,  deflections 
to  the  other  side  indicating  the  flow  in  the  opposite  direction.  In- 
struments deflecting  only  in  one  direction  are  simpler  in  construc- 
tion, and  this  fact  counterbalances  the  slight  inconvenience  attached 
thereto.  The  instrument  should  indicate  correctly  in  whatever 
position,  horizontal  or  vertical,  it  may  be  placed.  These  remarks 
require  certain  amplifications. 

1.  Upon  the  low  resistance  of  the  instrument  depends  to  a 
great  extent  its  delicacy;    this  delicacy  should,  for  diagnostic 
purposes,  be  such  that  -^  of  a  milliampere  will  be  indicated  upon 
the  scale,  and  y^nr  of  a  milliampere  may  be  estimated.     For  purely 
therapeutic  purposes  the  measurement  of  ^  of  a  milliampere  is 
sufficient. 

2.  The  instrument,  in  order  not  to  be  influenced  by  outside 
magnetism,  and  yet  to  be  sufficiently  sensitive,  should  have  no 
iron,  steel,  or  nickel  constituent  in  its  moving  parts,  and  the  perma- 
nent magnet  should  so  be  arranged  around  the  core  that  all  outside 
magnetism  is  neutralized. 

3.  The  division   of  the  scale  to  at   least  50  milliamperes 
would  be  impossible  on  a  segment  of  a  small  circle,  so  that  the 
use    of  shunts  must   be    resorted  to;  thereby  enabling  us  to 
measure  certain  known  parts  of  the  entire  current.     Thus,  -^  or 
Y-^J-  of  this  current  may  be  indicated  upon  the  scale,  in  which  case 
the  scale  divisions  must  be    multiplied  by  10  or  100  in  order  to 
obtain  a  reading. 

4.  In  the  instruments  formerly  employed,  the  magnetic  needle 
oscillated  to  and  fro  for  a  long  time  before  it  came  to  rest.     This  in 
itself  rendered  the  reading  difficult,  and  often  postponed  a  reading 
for  so  long  that  the  reading,  when  made,  did  not  correspond  (on 
account  of  the  lowered  resistance  of  the  body  produced  by  the 


158 


GALVANIC    APPARATUS    AND    ITS    USE 


flowing  current)  to  the  initial  closure  current  that  had  produced  a 
physiologic  reaction.  The  manner  of  making  an  instrument  aperi- 
odic, or  dead  beat,  has  already  been  described. 


FIG.  118. — FRONT  VIEW  OF  UPRIGHT  MILLIAMPEREMETER. 


FIG.   119. — SHOWING  TENSION  SPRING  OF  MILLIAMPEREMETER. 

An  excellent  instrument,  of  American  manufacture,  serviceable 
for  diagnostic  work,  and  that  possesses  all  the  requisites    stated, 


MILLI  AMPEREMETERS  159 

except  that  the  needle  is  deflected  in  one  direction  only,  is  made  by 
the  Wappler  Electric  Controller  Company,  of  New  York.  The 
mechanism  of  this  instrument  may  be  understood  from  the  accom- 
panying illustrations.  Figure  118  represents  a  front  view.  The 
permanent  magnet  5"  N  consists  of  four  pole  pieces.  A  soft-iron 
core,  C,  is  adjusted  between  the  pole  pieces  at  the  point  of  greatest 
density  of  the  magnetic  field.  An  armature,  A  (Fig.  1 19),  consist- 
ing of  a  small  copper  wire  bobbin,  swings  in  the  magnetic  field 
around  the  core  C.  The  permanent  field  is  adjusted  to  the  field  of 
the  bobbin,  N2—S2,  so  that  the  slightest  direct  current  traversing 


FIG.  1 20. — ANOTHER  FORM  OF  UPRIGHT  MILLIAMPEREMETER. 

the  wire  of  the  armature  produces  a  tendency  to  rotate  it.  This 
rotary  tendency  is  counteracted  by  two  tension  springs,  Pl  and  P2 
(Fig.  1 19),  through  which  the  current  enters  and  leaves  the  arma- 
ture. 

Flemming,  of  Philadelphia,  manufactures  a  milliamperemeter  con- 
taining resistance  coils  by  which  the  current  may  be  lessened  to 
TW  or  TFiF  Part>  and  in  which  the  needle  may  be  deflected  in  either 
direction  (Fig.  120).  It  is  approximately  accurate,  and  with  occa- 
sional readjustment  serves  a  useful  purpose. 

Very  convenient  and  reliable  are  the  aperiodic  horizontal  milli- 


i6o 


GALVANIC    APPARATUS    AND    ITS    USE 


amperemeters    devised    by    Eulenburg,     and     manufactured     by 
Hirschmann,  of  Berlin.     (See  Fig.  121.) 

Remarks  on  the  Practical  Choice  of  a  Milliamperemeter. 

Whoever  desires  to  make  use  of  a  galvanometer  for  the  purpose  of 
obtaining  measurements  of  currents  for  therapeutic  purposes  alone, 
and  does  not  desire  to  make  accurate  measurements  of  quantitative 
physiologic  reactions  for  diagnostic  purposes,  will  have  no  diffi- 
culty in  selecting  a  suitable  instrument.  A  slight  degree  of  inac- 
curacy is  of  no  significance  in  electrotherapy,  for  the  therapeutic 


FIG.  121. — HORIZONTAL  MILLIAMPEREMETER. 


action  of  a  current  is  not  altered  by  variations  of  ^  of  a  milliam- 
pere. 

A  vertical  instrument  presents  the  advantage  of  easier  direct 
reading  than  does  a  horizontal  one ;  on  the  other  hand,  vertical 
galvanometers  with  permanent  magnets  become  unreliable  in  con- 
sequence of  changes  in  the  magnetism  of  the  needles,  and  must, 
therefore,  be  recalibrated  every  few  years.  For  ordinary  practical 
use  I  find  the  advantages  of  direct  reading  over  indirect  reading 
by  means  of  reflection  in  a  mirror  so  great  that  I  am  willing  to  put 
up  with  the  inconvenience  of  recalibration. 


VOLTMETERS  l6l 

Whenever  absolute  accuracy,  reliability,  and  permanency  of  cali- 
bration are  desirable,  the  horizontal  galvanometer  should  be  se- 
lected. The  best  instruments  of  this  type  of  which  I  have  prac- 
tical knowledge  are  the  Weston  meter,  described  on  page  85, 
calibrated  in  milliamperes,  Hirschmann's  instrument,  and  the  one 
made  by  the  Wappler  Company. 

Horizontal  galvanometers  with  cocoon-thread  suspension  are 
not  adapted  for  general  use,  on  account  of  the  trouble  encountered 
in  setting  them  up,  and  on  account  of  the  facility  with  which  the 
thread  becomes  disordered  or  tears.  Horizontal  instruments  with 
simple  point  suspension  should  be  entirely  discarded.  The  neces- 
sary wear  and  tear  upon  the  suspension  points  rapidly  renders  them 
inaccurate. 

Voltmeters. 

It  becomes  more  and  more  apparent,  especially  in  electrodiag- 
nostic  and  electrophysiologic  experiments,  that  the  regulation  of 
the  voltage  of  a  galvanic  current  is  of  greater  importance  than  the 
regulation  of  current  strength  by  means  of  interposed  resistance. 
The  arguments  that  for  years  have  been  advanced  in  favor  of  the 
use  of  an  absolute  meter  of  the  current  strength  employed  in 
medicine,  and  that  have  forced  its  universal  adoption,  may  be  ap- 
plied, mutatis  mutandis,  to  the  use  of  a  meter  for  determining  the 
pressure  of  the  current  employed ;  and  there  is  no  doubt  in  my 
mind  that  in  a  very  few  years  the  use  of  a  voltmeter  by  physicians 
and  physiologists  will  be  quite  as  universal  as  is  the  present  use  of 
the  galvanometer. 

The  principles  underlying  the  construction  of  voltmeters  have 
already  .been  stated.  If  the  resistance  of  a  milliamperemeter  be 
increased  up  to  1000  ohms,  it  can,  without  further  change,  be  used 
to  measure  electromotive  force,  for  as  a  current  of  one  volt  pro- 
duces one  milliampere  in  1000  ohms,  the  milliamperes  are 
equal  to  the  volts  so  long  as  the  resistance  in  the  circuit  is  1000 
ohms. 

Any  galvanometer  of  sufficiently  high  resistance  may,  therefore, 
be  calibrated  in  volts  and  be  used  as  a  voltmeter.  In  the  use  of 
the  voltmeter  neither  the  body  of  the  patient  nor  any  other  unknown 
ii 


l62 


GALVANIC    APPARATUS    AND    ITS    USE 


resistance  must  be  in  the  circuit  while  the  electromotive  force  of 
the  source  is  being  measured. 

Reliable  voltmeters  are  made  by  all  manufacturers  of  indus- 
trial electric  instruments.  The  Weston  and  the  Jewell  meters  are 
those  that  I  know  best.  The  Jewell  meter  is  manufactured  by 
the  Mclntosh  Battery  Company,  of  Chicago,  and  is  shown  in  figure 
122.  This  meter  is  made  according  to  the  principles  here  advo- 
cated, with  a  coil  moving  in  the  field  of  a  permanent  magnet.  It 


FIG.  122. — JEWELL  VOLTMETER. 

has  a  resistance  of  about  120  ohms  to  each  volt  of  scale,  so  that 
a  meter  capable  of  registering  from  o  to  150  volts  has  a  resistance 
of  18,000  ohms. 

Electrodes. 

For  the  application  of  a  current  to  the  body  for  diagnostic  or 
therapeutic  purposes,  specially  adapted  end-pieces,  or  electrodes, 
are  necessary.  These  may  be  made  of  various  materials  and  shapes, 
according  to  the  place  of  application  for  which  they  are  designed. 
For  all  purposes  that  require  uniformity  of  application  and  pressure, 


ELECTRODES 


163 


the  electrode  is  furnished  with  a  handle ;  in  such  cases  the  material 
that  constitutes  the  electrode  must  be  sufficiently  rigid  not  to 
bend  when  pressure  is  exerted,  and  therefore  only  a  hard  metal 
should  be  used.  Yet  their  rigidity  may  be  regulated  by  the 
thickness  of  the  metal  employed,  so  that  if  it  is  desirable  to  give 
them  an  individual  shape  for  certain  purposes,  this  may  be  done  by 
using  a  metal  sheet  that  is  so  thin  that  it  is  capable  of  being  bent 
by  hand,  but  that  is  yet  of  sufficient  firmness  to  retain  the  shape 
that  has  thus  been  given  it,  despite  a  fair  degree  of  pressure  exerted 
on  it  through  the  handle. 

Electrodes  that  are  to  be  applied  to  the  body  directly  by  the 
hand  of  the  operator  or  by  means  of  a  broad  band  may  be  made 


FIG.  123.— ELECTRODE  HANDLE. 


FIG.  123  A. — ELECTRODE  HANDLE. 

of  flexible  metallic  lead,  amalgam  of  tin,  or  wire  netting,  and  thus 
adapt  themselves  more  easily  to  the  surface  of  the  body.  The 
handle  of  the  electrode  may  be  made  the  carrier  of  various  con- 
trivances for  making,  breaking,  and  reversing  the  current  or  for  con- 
trolling it.  This  handle  is  made  of  some  insulating  material,  usu- 
ally hard  rubber  or  wood,  and  should  be  so  formed  as  to  be  grasped 
easily.  Into  the  end  of  the  handle  is  fixed  a  metal  piece  bearing 
a  binding  screw  and  a  metal  rod,  to  which  the  electrode  is  fastened, 
or  the  metal  rod  bearing  the  electrode  at  one  end  may  be  made  to 
pass  through  the  insulating  handle  and  have  its  binding  screw  for 
the  attachment  of  the  conducting  cord  at  the  other  end.  Figure 
123  shows  the  first  form  of  handle  and  figure  123  A  the  second. 


150  '' 


MEYROWITZ 


50 


50 


164  FIG.  124. — VARIETIES  OF  ELECTRODES. 


18  13  14      15      16  17          7 


20 


19 


FIG.   124  A. — INTERRUPTING  HANDLE  AND  VARIOUS  ELECTRODES. 
Eustachian.      2.  Eye.      3.  Tongue.      4.   Ear.      5.  Nasal   or  laryngeal.      6.  Inter- 
rupting  handle.     7.   Special    nerve.     9.   Uterine    and   rectal.     10.   Urethral.      u. 
Cup-shaped  for  os  uteri.     12.  Vaginal.     14,  15,  1 6.  Olives,  points,  etc.     17.  Carbon 
disk.      18.  Wire  brush.      19.  Foot-plates.     20.  Spinal. 

I65 


1 66 


GALVANIC    APPARATUS    AND    ITS    USE 


FIG.  1246. — ABDOMINAL  AND  OTHER  PADS.     AURAL  ELECTRODE. 

The  electrode  itself  may  be  made  of  various  forms,  flat  and  in 
that  case  circular,  square  or  oblong,  ball  shaped  or  conic  ;  be  made 
of  metal  or  carbon  ;  and  be  bare  or  covered.  If  bare,  it  is  used  as 
a  dry  electrode  ;  if  covered,  it  is  covered  permanently  or  at  the 
time  of  application  with  sponge,  cotton,  clay,  or  other  material  that 
may  be  saturated  with  water,  and  is  used  as  a  moist  electrode. 
Cotton  is  easily  wrapped  about  the  carbon  or  metal  terminal  of  an 


FIG.  125. — WIRE  BRUSH  ELECTRODE. 


electrode,  and  as  this  may  be  freshly  done  each  time  the  instrument 
is  used,  makes  a  very  cleanly  covering. 

Electrodes  of  various  shapes  are  shown  in  figures  1 24,  1 24  A,  and 
124  B.  Figure  125  shows  a  bare  electrode  consisting  of  wires  of 
brass  or  metal  bound  together  in  the  form  of  a  brush.  It  is  known 
as  a  wire  brush.  An  assortment  of  such  electrodes,  varied  not 
only  in  form,  but  also  in  size,  should  form  part  of  every  electro- 
diagnostic  and  electrotherapeutic  outfit.  The  flat  electrodes  should 


UNPOLARIZABLE  ELECTRODE  l6/ 

have  the  area  of  their  covered  surface  marked  upon  them.  Ball 
electrodes  should  be  supplied  in  diameters  of  i,  2,  and  3  cm.  when 
covered. 

In  the  application  of  electricity  to  the  surface  of  the  body,  elec- 
trolytic action  takes  place  in  the  parts  of  the  body  traversed 
by  the  current ;  the  alkaline  constituents  of  the  decomposed  tissue 
fluids  accumulate  at  the  negative  electrode,  the  acid  constituents 
at  the  positive  electrode.  These  products  of  decomposition  act 
deleteriously  upon  the  skin,  and  alter  the  electrode  itself  so  as  to 
interfere  with  accurate  scientific  investigation.  For  these  reasons  the 
exclusive  use  ofunpolarizable  electrodes  was  recommended 
by  the  Paris  International  Congress  of  1881.  This  recommendation 
is  too  far-reaching,  but  must  be  subscribed  to  in  so  far  as  scientific 
investigations  and  persons  with  susceptible  skin  are  concerned.  It 
is  always  necessary,  however,  to  give  due  regard  to  the  coverings 


FIG.  126. — UNPOLARIZABLE  ELECTRODE. 

of  the  electrode,  to  see  that  they  are  clean  and  not  worn,  and,  above 
all,  to  be  careful  that  no  metal  part  shall  come  in  direct  contact 
with  the  skin. 

An  unpolarizable  electrode  is  shown  in  figure  126.  The 
detachable  handle  carries  a  bell  glass,  into  which  protrudes  a  zinc 
rod  that  is  metallically  connected  with  the  binding  screws.  This 
bell  glass  is  filled  with  a  solution  of  zinc  sulphate,  and  is  closed  by 
means  of  "a  stopper  of  clay  or  papier-mache  enveloped  in  two  folds 
of  linen. 

The  direct  application  of  electricity  to  the  various  body-cavities 
is  effected  by  specially  constructed  electrodes.  Their  number  is  so 
great  that  it  is  unprofitable  even  to  mention  them  all,  much  less 
shall  we  attempt  to  give  a  description  of  them. 

The  handle  is  best  made  detachable  from  the  electrode  itself, 


i68 


GALVANIC    APPARATUS    AND    ITS    USE 


and  it  then  possesses  the  practical  advantage  that  one  handle  can 
be  utilized  for  many  attachment  pieces.  The  attachment  mechanism 
between  handle  and  electrode  usually  consists  of  a  screw  and  nut, 
the  one  or  the  other  being  upon  the  handle  or  upon  the  end  of  the 
electrode.  This  variability  in  construction,  as  well  as  the  fact  that 
different  screw-threads  are  used  by  different  manufacturers,  often 
renders  it  impossible  to  utilize  the  handle  for  any  but  the  electrodes 


FIG.  127. — COMBINATION  ELECTRODE  HANDLE. 

made  by  the  manufacturer  of  the  handle.  To  obviate  this  difficulty 
I  designed,  many  years  ago,  a  combination  handle  that  admits 
of  the  use  of  any  electrode  having  a  metal  attachment  end,  en- 
tirely regardless  of  the  size  or  construction  of  this  end.  This 
handle  is  shown  in  figure  127.  It  consists  of  a  double  workman's 
chuck,  A,  inserted  into  a  hard-rubber  cylinder,  B,  to  the  ends  of 
which  are  screwed  small  cylinders,  C  and  D,  beveled  longitudinally 
upon  their  interior.  Through  these  the  metal  chuck  also  passes. 


FIG.  128. — INTERRUPTING  ELECTRODE  HANDLE. 

The  further  the  cylinders  C  and  D  are  screwed  down,  the  more  do 
the  chuck  ends  become  compressed,  and  the  smaller  does  the 
opening  become.  The  method  of  use  of  these  handles  is  first  to 
loosen  the  end  cylinders  until  the  openings  in  the  chuck  are  suffi- 
ciently large  to  admit  of  the  introduction  of  the  end-piece  of  the 
electrode  at  one  terminal,  and  the  binding  piece  of  the  conducting 
cord  at  the  other  ;  then  the  cylinders  are  screwed  down  until  the 
inserted  electrode  and  conducting  cord  are  firmly  held. 


INTERRUPTING,  REVERSING,  AND    CONTROLLING    HANDLES         169 


The 


handle,  as  already  mentioned,  may  also  be  made  the  carrier 
of  a  current  interrupter,  reverser,  or 
controller. 

The  interrupting  electrode  that  I 
consider  the  best  is  shown  in  figure  128, 
and  a  new  and  practical  pole-changing 
and  current-controlling  electrode,  made 
for  me  by  the  Wappler  Company,  is 
shown  in  figure  129.  Both  these  illus- 
trations explain  themselves. 

Usually,  in  electrodiagnostic  and  elec- 
trotherapeutic  work  it  is  desirable  to 
attach  one  electrode  firmly  to  the 
body  of  the  patient,  so  that  while  manip- 
ulating the  other  the  operator  may 
have  a  free  hand  for  the  regulation  of 
the  current,  etc.  Such  fastening  may 
be  accomplished  by  means  of  an  elastic 
belt  or  by  means  of  hard-rubber  springs. 
The  latter  possess  the  advantage  that, 


FIG.   130. — ELECTRODE  WITH  HARD-RUBBER 
SPRING  ATTACHMENT. 


FIG.  129.  —  POLE-CHANGING 
AND  CURRENT-CONTROL- 
LING HANDLE. 


FIG.  131. — ELECTRODE  WITH  ELASTIC  BELT 
ATTACHMENT. 


I7O  GALVANIC    APPARATUS    AND    ITS    USE 

by  means  of  heat,  they  may  be  given  any  desired  shape  or  strength 
of  spring  (Figs.  130  and  131). 

Conducting  Cords. 

Conducting  cords  are  used  to  make  a  connection  between  the 
electrode  handle  and  the  source  of  current  supply.  They  consist 
of  a  conducting  wire  or  wires  covered  with  some  insulating  mate- 
rial, and  are  furnished  with  rigid  metal  ends  by  means  of  which 
they  may  be  firmly  connected  with  the  binding  posts  of  the  battery. 
Such  a  conductor  should  be  made  up  of  a  cable  of  many  copper  or 
brass  wires,  and  be  so  flexible  that  the  entire  cord  presents  no 
inconvenience  on  account  of  rigidity.  Their  length  should  be  at 
least  i  ^  meters,  and  the  insulating  coverings  should  be  of  differ- 
ent colors — red  and  green  or  red  and  black — for  the  two  cords 
employed,  so  that  they  can  easily  be  followed  by  the  eye  from  the 
electrode  to  the  battery,  and  thus  the  pole  of  the  electrode  be 
recognized. 


CHAPTER  III 

SOURCES  OF  CURRENT  SUPPLY  FOR  DIAGNOSTIC 

AND   THERAPEUTIC    PURPOSES,  AND  THE 

APPARATUS  NECESSARY  FOR  ITS  USE 

Requirements  of  Stationary  and  Portable  Batteries.  Different  Types  of 
Cells.  Pole  Testers.  Care  of  Apparatus.  Causes  and  Remedies  of 
Disorder.  Currents  from  Central  Stations.  Direct  and  Alternating 
Currents.  Dangers  of  High  Voltage  Currents.  Leakage  Currents. 
Controlling  Apparatus.  Transformed  Systems.  Breakdown  of  Insula- 
tion. Safeguards.  Sudden  Increase  of  Current.  Compound  Shunt. 
Method  of  Using  Street  Currents.  Limit  Resistance.  Rheostat.  Au- 
thor1 s  Method. 

APPARATUS. 

The  prime  essentials  of  an  apparatus  for  electrodiagnostic 
and  electrotherapeutic  purposes  are  as  follow  :  The  source  of 
supply  must  have  a  sufficient  electromotive  force  and 
be  of  fair  constancy;  a  current  controller,  preferably 
a  selector  or  volt  controller  and  rheostat,  a  pole 
changer,  and  a  galvanometer  must  be  available  in  the 
circuit. 

The  source  of  supply  may  be  from  a  central  station  (electric 
light,  etc.)  or  from  a  battery.  Over  the  currents  supplied  by  the 
electric  light  and  power  companies  the  physician  has  no  direct 
control.  He  can  modify  them  only  after  they  reach  his  apparatus. 
Considerations  of  various  kinds,  however,  may  govern  the  choice 
of  a  battery. 

Batteries  and  Cells. 

In  addition  to  being  fairly  constant  and  furnishing  a  current  of 
sufficient  intensity  the  battery  should  be  durable,  and  at  the 
same  time  of  such  simple  construction  that  all  its  parts  are 
readily  accessible  and  can  be  kept  clean  and  in  repair  by  the 
physician  himself;  furthermore,  the  original  cost,  as  well  as 

171 


CURRENT   SUPPLY    AND    APPARATUS 

the  cost  of  maintenance,  should  be  moderate.  The  frequent 
necessity  of  transporting  the  apparatus  to  the  patient's  bedside 
requires  that  one  form  shall  be  small,  light,  and  easily 
portable. 

The  electromotive  force  of  the  battery  must  be  sufficiently 
great  to  furnish  20  milliamperes  against  a  resistance  of  5000 
ohms.  For  certain  special  purposes  from  3  to  5  milliamperes 
may  suffice,  while  for  others  (gynecologic  work)  many  more 
are  necessary.  Theoretically,  we  should  therefore  prefer  cells  of 
high  electromotive  force  and  slight  internal  resistance  ;  but  consid- 
ering the  high  resistance  of  the  human  body,  this  is  not  essential, 
and  cells  with  less  surface  of  elements,  and  which,  therefore,  are 
smaller  and  have  a  higher  internal  resistance,  such  as  the  Leclanche, 
will,  for  other  reasons,  be  found  more  efficient.  In  order  to  obtain 
sufficient  current  strength  a  battery  must  be  made  of  a  large 
n  u  m  b  e  r  of  cells.  Stationary  batteries  with  D  a  n  i  e  1 1  cells  require 
at  least  from  50  to  60  cells,  while  if  Leclanche  cells  be  used,  40 
will  suffice.  A  portable  battery  should  have  40  Leclanche  or 
silver  chlorid  cells,  or  30  potassium  bichromate  cells. 

As  regards  the  constancy  of  the  battery,  it  is  necessary  that, 
with  an  interposed  resistance  equal  to  that  of  the  human  body,  the 
current  strength  should  remain  unaltered  for  at  least  fifteen  min- 
utes. This  may  be  taken  as  the  maximum  service  required  of  a 
battery  at  any  one  time,  while  usually  a  very  much  shorter  period 
will  suffice,  and  in  electrodiagnosis  momentary  currents  only  are 
required.  For  this  reason,  and  because  by  means  of  a  proper 
system  of  current  control  and  a  milliamperemeter  the  current  can 
always  be  kept  at  a  certain  strength,  no  matter  how  inconstant  a 
battery  may  be,  I  lay  less  stress  upon  the  constancy  of  the  battery 
than  is  usually  done. 

For  portable  batteries  the  cells  will,  of  course,  be  as  small  as 
possible,  leaving  all  other  qualities  aside,  and  for  this  reason  such 
cells  as  the  Grenet  and  dry  cells,  which  would  be  unfit  for  use 
in  a  stationary  battery,  may  here  be  used. 

Stationary  batteries,  on  the  other  hand,  must,  above  all,  be 
durable  and  reliable,  while  the  size  is  of  less  importance.  There- 
fore other  qualities  of  the  individual  cells  may  be  considered. 


PORTABLE  AND  STATIONARY  BATTERIES  1/3 

So,  in  a  portable  battery,  the  current  controller  and  reverser 
may  be  affixed  to  the  electrode  handle  and  the  galvanometer  be 
detachable  from  the  apparatus,  while  in  a  stationary  battery  all 
these  appliances  should  form  an  integral  part  of  the  machine,  as  it 
will  also  be  found  practicable  to  combine  the  faradaic  coil,  as  well 
as  any  other  apparatus  (sinusoidal),  on  one  and  the  same  base 
with  the  other  parts  of  the  apparatus. 

Cells. 

The  choice  of  a  cell  will  depend  upon  the  purpose  for  which  it 
is  to  be  employed — whether  for  a  stationary  or  for  a  portable 
battery,  and  whether  the  current  is  to  be  directly  applied  to 
the  body  or  is  to  be  used  for  cautery  and  light. 

Any  cell  of  fair  electromotive  force  and  constancy  may  be  em- 
ployed for  diagnostic  and  therapeutic  purposes ;  yet  certain  cells 
possess  material  advantages  over  others. 

For  stationary  batteries  the  gravity  cells  have  been  largely 
used,  but  in  my  opinion  they  are  entirely  unsuited  for  the  practical 
requirements  of  a  physician.  They  are  exceedingly  dirty,  in  conse- 
quence of  the  constant  accumulation  and  creeping  of  the  zinc  sul- 
phate, and  the  frequency  with  which  they  must  be  refilled  makes  them 
untrustworthy.  Evaporation  rapidly  breaks  the  circuit  by  lowering 
the  water  surface  below  the  horizontally  suspended  zinc.  The  cells 
best  suited  for  a  stationary  battery  are  of  the  open  circuit  type, 
and  of  these,  the  one  that  I  have  found  most  advantageous  is  the 
Lee  lane  he,  of  one  form  or  another,  either  the  prism  or  gonda 
pattern.  For  all-around  work — galvanization,  electrolysis,  etc. — I 
know  of  no  cell  that  will  give  so  much  satisfaction.  Its  electro- 
motive force  is  high,  and  its  internal  resistance  is  moderate. 

So  long  as  the  cell  is  not  in  action  there  is  little  chemical  decom- 
position, as  the  circuit,  then,  is  open.  Theoretically,  there  should 
be  none.  The  cell  is  always  ready  for  use,  and  if  well  constructed, 
will  last  for  some  two  years  without  other  attention  than  an  occasional 
refilling  with  water.  These  cells,  furthermore,  are  so  simple  and 
so  easily  managed  that  they  may  be  cleansed  and  refilled  without 
expert  assistance. 

Portable  Batteries. — Highly  as  Leclanche  cells  are  to  be  rec- 


174  CURRENT   SUPPLY    AND    APPARATUS 

ommended  for  use  in  stationary  batteries,  they  give  little  satisfac- 
tion for  portable  use.  This  results  from  their  necessary  diminution 
in  size.  The  smaller  such  a  cell  is  made,  the  more  unsatisfactory 
does  it  become.  Test-tube  Leclanche  cells  have  been  combined 
into  portable  batteries,  but  their  constancy  is  so  problematic  and 
their  local  action  is  so  great,  that  such  batteries  give  no  satisfaction 
at  all. 

Dry  cells  (really  an  improved  form  of  Leclanche)  are  quite 
desirable  for  portable  batteries,  on  account  of  the  impossibility  of 
spilling  and  oxidation.  Such  cells,  if  not  too  small,  are  sufficiently 
constant  for  all  medical  purposes,  and,  having  a  capacity  of  as  much 
as  4  ampere-hours,  would  last  for  4000  applications  of  6  milli- 
amperes  of  current  and  often  minutes'  duration  each.  The  only 
objection  to  such  batteries  is  from  an  economic  point  of  view ;  for 
the  cells  once  exhausted,  cannot  be  replenished,  but  must  be 
replaced  by  new  ones. 

When  a  specially  small  cell  is  required,  or  whenever  the  restric- 
tion of  the  size  of  a  battery  to  a  minimum  is  desirable,  there  can 
be  no  better  selection  than  the  silver  chlorid  cell.  Such  cells 
are  most  thoroughly  depolarizing,  and  can,  therefore,  be  made 
smaller  than  any  other  without  sacrifice  of  constancy.  They  have 
an  electromotive  force  of  1.61  volts,  and  a  low  internal  resis- 
tance ;  they  are  always  ready  for  use,  are  not  in  action  when  the 
circuit  is  open,  and  are  so  sealed  that  no  fluid  can  escape  by  shak- 
ing or  with  moderately  rough  usage.  The  objection  to  these  cells 
is  the  expense  of  refilling. 

Potassium  bichromate  cells  possess  certain  advantages  for 
portable  batteries  that  make  their  use  desirable,  especially  for 
country  work,  where  the  services  of  an  electrician  are  not  usually 
obtainable,  and  for  those  who  have  but  infrequent  use  for  a  battery 
of  any  kind.  In  the  first  place,  they  can  easily  be  refilled  and 
cleansed  by  the  inexperienced  ;  such  a  battery  that  has  stood  un- 
used for  months  may  be  cleansed,  refilled,  and  put  in  good  work- 
ing order  again  in  about  one  hour.  Furthermore,  they  have  a  very 
high  electromotive  force — 2  volts — and  less  than  0.05  ohm  of 
internal  resistance,  so  that  two  cells  are  about  equal  in  practical 
medical  work  to  three  cells  of  the  Leclanche  type  ;  thus  the  bat- 


TESTS    FOR    POLARITY  1/5 

tery  may  be  considerably  smaller.  They  are  also  particularly  useful 
for  the  strong  current  required  for  electrolysis.  The  zincs  last 
for  a  number  of  years  when  used  only  for  average  bedside  work, 
and  can  be  replaced  easily.  Various  solutions  may  be  used  as 
electrolytes.  The  preferable  solution  is  the  following  : 

Potassium  bichromate I  part 

Water, 20  parts 

Strong  sulphuric  acid, 2  parts 

Mercury  bisulphate, I  part. 

To  cleanse  the  cells,  the  vessels  should  be  filled  with  water,  and 
the  elements  should  be  left  to  soak  in  them  overnight,  so  as  to 
dissolve  all  the  crystals  that  may  have  formed.  The  disadvantage 
of  these  cells  is  that  they  must  have  plunge  elements,  and  the 
mechanism  by  which  the  plunging  is  effected  frequently  becomes 
disordered.  The  vessels  cannot  be  closed  effectually,  and  in  conse- 
quence evaporation  and  spilling  of  the  fluid  are  not  guarded  against. 
If  the  battery  is  in  daily  use,  it  must  be  cleansed  and  refilled  about 
once  in  every  three  months. 

The  purpose  for  which  the  cells  are  to  be  used  will  determine  the 
manner  of  their  arrangement. 

The  number  of  different  kinds  of  stationary  and  portable  batteries 
manufactured  for  medical  purposes  is  veiy  large,  and  each  one  may 
have  some  special  point  in  its  favor.  It  is,  however,  impracticable 
and  useless  to  enumerate  the  various  kinds  in  the  market,  as  the 
principles  governing  their  construction  have  been  given  at  ample 
length.  The  catalogues  of  manufacturers  may  be  consulted  to 
determine  in  how  far  these  principles  have  been  carried  out. 

Tests  for  Polarity. 

The  cells  having  been  arranged  into  a  battery,  the  terminals 
of  the  first  carbon  and  that  of  the  last  zinc  must  each  be  joined 
to  a  binding  post  upon  the  plate  of  the  apparatus  used.  These 
binding  posts  then  become  the  positive  and  negative  poles 
respectively,  and  serve  for  the  reception  of  the  ends  of  the  con- 
ducting cords.  These  poles  are  usually  marked  +  and  — ,  but 
often,  through  some  error  of  connection,  the  polarity  has  become 
changed  or  the  posts  may  have  been  marked  incorrectly  ;  it  is, 


176  CURRENT    SUPPLY    AND    APPARATUS 

therefore,  necessary  to  test  the  polarity  of  the  posts  before 
using  the  battery.  The  poles  of  the  battery  may  be  determined  as 
follows :  The  two  metal  ends  of  the  terminal  wires  being  placed 
upon  a  piece  of  moistened  litmus  paper,  the  anode  will  turn 
the  paper  red,  while  the  kathode  gives  it  a  deep  blue  color. 
If  instead  of  litmus  paper  a  mixture  of  potassium  iodid  and 
starch  paste  is  used,  the  anode  causes  a  deep  blue  coloration. 


FIG.  132. — POLE  TESTER. 

When  a  great  deal  of  pole  testing  is  to  be  done,  as  when  the  cur- 
rent is  obtained  from  the  main  (because  the  dynamo  may  at  any 
time  be  reversed  without  our  knowledge),  it  is  convenient  to  have  a 
special  pole  tester.  I  have  had  constructed  two  that  are  admir- 
able in  their  simplicity  and  trustworthiness.  The  testing  agent  here 
employed  is  phenol-phthalein.  One  of  the  devices  consists  of 
a  glass  tube  filled  with  a  solution  of  phenol-phthalein  and  sealed. 


FIG.  133. — POLE  TESTER. 


In  each  end  of  the  tube  is  a  piece  of  platinum  wire  that  passes 
through  the  glass  into  the  fluid,  while  the  outer  ends  are  connected 
with  binding  posts  (Fig.  132).  The  fluid  surrounding  the  kathode 
turns  a  bright  red  upon  passage  of  the  current.  The  agitation 
of  the  liquid  causes  the  red  color  to  disappear. 

In  the  other  device,  figure  133,  a  paste  of  chalk,  plaster-of- 
Paris,  and  phenol-phthalein  is  held  in  a  form  of  hard  rubber. 


CARE    OF    BATTERIES  1 77 

For  use  the  paste  is  slightly  moistened  and  the  wires  are  applied, 
when  the  red  color  at  once  indicates  the  negative  pole. 

When  none  of  the  foregoing  indicators  is  available,  the  wires  may 
be  placed  in  a  glass  ofwater,  and  the  large  number  of  b  u  b  b  1  e  s 
arising  from  one  wire  will  indicate  the  jgt&aasaatifr  pole;  or  the  elec- 
trode may  be  applied  to  the  tongue,  when  a  weak  alkaline 
taste  will  indicate  the  kathode,  a  markedly  acid  one,  the 
anode.  In  neither  of  these  methods  should  a  strong  current  be 
used. 

Care  of  Battery. 

No  matter  how  well  constructed,  every  electric  apparatus  requires 
a  certain  amount  of  care  and  attention.  The  physician  who 
knows  thoroughly  every  detail  of  the  mechanism  of  the  appa- 
ratus with  which  he  is  working,  being  able,  if  necessary,  to  take 
it  apart  and  put  it  together  again,  will  derive  more  satisfaction 
from  an  inferior  apparatus  than  will  he  who  does  not  possess  this 
knowledge  obtain  from  one  that  is  actually  much  better  in  every 
way.  Simplicity  of  construction  is,  therefore,  a  great  advan- 
tage ;  the  fewer  screws,  wires,  and  connecting  points  there  are,  the 
more  readily  will  the  physician  be  able,  in  an  emergency,  to  repair 
slight  disorders  of  function,  and  the  less  likely  are  such  disorders 
to  take  place. 

Location  of  Disorder. — Should  disorder  occur  and  the  current 
grow  suddenly  weak  or  fail  entirely,  the  source  of  trouble  should 
at  once  be  sought.  It  has  been  my  experience  that  in  the  majority 
of  cases  imperfection  or  failure  in  the  current  flow  is  due  to  dis- 
ordered contact  at  some  point  of  the  circuit.  Hence  a  system- 
atic search  should  be  made,  and  the  entire  circuit  be  examined. 

It  is  best  to  begin  with  the  connection  between  the  body  of  the 
patient  and  the  battery,  then  to  examine  the  instruments  upon  the 
base  of  the  apparatus,  and  finally  to  inspect  all  connections  under 
the  base  and  in  the  source  of  supply  itself.  It  will  most  often  be 
found  that  (i)  the  electrodes  are  not  sufficiently  mois- 
tened, and  that,  on  account  of  insufficient  contact  between  elec- 
trode and  body,  the  necessary  amount  of  current  cannot  pass.  The 
remedy  is  obvious — viz.,  thorough  saturation  of  the  covering  of  the 


1/8  CURRENT   SUPPLY    AND   APPARATUS 

electrodes,  preferably  with  warm  or  salt  water.  (2)  There  may  be 
a  break  in  the  wire  of  the  conducting  cords.  Such  breaks 
usually  take  place  at  the  part  where  the  wire  is  attached  to  the 
insertion  piece  of  the  cord  ;  a  break  may  also  occur  within  the  insu- 
lating covering.  A  test  made  after  the  removal  of  the  insertion 
piece  or  the  substitution  of  the  entire  cord  by  another,  and  notation 
of  the  galvanometer  deflection,  will  show  the  seat  of  trouble  if  it  lie 
in  the  two  cords. 

If  no  disorder  be  found  in  electrodes  or  conducting  cords,  the 
apparatus  on  the  base  must  be  scrutinized.  Here  the  most 
frequent  disorders  are  :  ( I )  The  loosening  of  a  screw;  therefore 
all  screws  should  be  tightened.  (2)  Switches,  contact  but- 
tons, plugs,  and  plug  holes  become  tarnished,  corroded, 
or  dusty,  and  thus  interfere  with  perfect  contact.  A  little  vaselin 
or  oil  will  remedy  this.  (3)  The  galvanometer  is  frequently 
connected  to  the  base  by  means  of  a  metal  spring,  and  this 
connection  may  have  become  loosened.  (4)  The  faradaic  cur- 
rent usually  fails  because  the  interrupter  works  badly.  Usu- 
ally it  does  so  because  the  contact  between  the  screws  and 
contact  plate  has  become  deranged.  A  proper  adjustment  of  the 
screw  will  remedy  this.  Or  it  may  fail  because  the  contact  plate 
has  become  oxidized,  in  which  case  the  oxid  may  easily  be 
removed  with  a  file. 

No  disorder  having  been  found  above  the  base,  an  examination 
of  the  cells  and  their  connections  should  follow.  Here  the 
disturbance  will  usually  be  found  in  the  cells  themselves.  Such 
disturbances  are  due  to  lack  of  water  surrounding  the  elements, 
or  to  the  zinc  being  so  badly  eaten  that  it  must  be  replaced. 

Any  disorder  in  the  wire  attachments  of  the  cells  can  be 
remedied  easily. 

CURRENTS  FROM  CENTRAL  STATIONS. 
Whenever  a  current  from  a  central  station  can  be  obtained, — that 
is,  whenever  electric  wires  for  lighting  or  powe.r  are  easily 
accessible, — the  physician  can  well  dispense  with  the  always 
more  or  less  troublesome  and  inconvenient  cells,  and  obtain  all  the 
advantages  of  an  unlimited  supply  either  by  using  such  currents 


DYNAMO    CURRENTS 

directly  or  by  charging  secondary  (storage)  cells  and  then 
deriving  his  therapeutic  or  diagnostic  current  from  these. 

Dynamo  Currents. 

At  first  impression  it  seems  foolhardy  to  use  for  medical  purposes 
an  electric  current  that  has  caused  so  many  and  so  serious  acci- 
dents. The  convenience  of  this  source  of  electricity  is,  however, 
so  great  that  if  it  can  be  shown  that  the  dynamo  current  can  so  be 
regulated  that  its  employment  will  be  unattended  by  danger,  every 
physician  who  has  access  to  such  a  current  will  undoubtedly  desire 
to  use  it. 

The  current  that  is  easiest  to  use  is  the  one  employed  for  lighting 
incandescent  lamps,  as  that  is  furnished  directly  to  all  modern 
houses. 

For  lighting  lamps  both  direct  and  alternating  currents 
are  employed. 

The  direct  current  dynamos  deliver  a  current  that,  to  all  intents 
and  purposes,  is  constant,1  and  that  practically  differs  in  no  way 
from  a  battery  current.  It  will  serve  fully  the  purposes  of  the  phy- 
sician. 

The  alternating  current,  on  the  other  hand,  is  lacking  in  elec- 
trolytic quality,  and  requires  a  transformer  for  cutting  down  the 
voltage,  and  a  commutator  for  turning  the  alternating  current 
into  a  unidirectional  one  before  it  can  be  made  available  for  our 
purposes. 

In  New  York  city,  the  direct  current  delivered  to  us  is  the  Edi- 
son current,  which  is  received  at  a  pressure  of  no  volts  approxi- 
mately. It  is  this  current  to  which  reference  is  had  here  unless 
some  other  is  specially  mentioned.  In  considering  the  physical  laws 
governing  this  current,  all  that  has  been  said  concerning  battery 
currents  will  apply,  except  that,  inasmuch  as  we  have  no  internal 
resistance  to  deal  with,  we  can,  from  our  iiovolt  source  of  supply, 
obtain  an  extremely  strong  and  intense  current  if  little  resistance 
be  placed  in  the  circuit,  and  it  need  hardly  be  said  that  by  interpos- 

1  Ample  experiments  have  been  made,  proving  that  nothing  need  be  feared  on  account 
of  the  inconstancy  of  the  current,  as  is  shown  by  the  steadiness  of  the  galvanometer 
needle. 


ISO  CURRENT    SUPPLY    AND    APPARATUS 

ing  sufficient  resistance  we  can  prevent  any  current  whatever  from 
passing. 

We  therefore  see  that  the  regulation  of  our  current  is  prac- 
tically entirely  a  question  of  interposed  resistance. 

Before  proceeding  with  the  description  of  the  apparatus  used  for 
control  of  the  current  pressure  and  current  quantity,  let  us  directly 
answer  the  question  that  is  asked  daily :  Is  there  no  danger  in  the 
use  of  an  electric-light  current  ?  There  certainly  is. 

Any  uninsulated  conductor  through  which  the  current  is  passing 
may  be  held  in  the  hand  without  other  danger  than  is  due  to  the 
overheating  of  the  wire.  If,  however,  the  current  be  one  of  high 
voltage,  and  a  complete  circuit,  of  which  the  body  forms  a  part,  be 
thereby  established,  there  may  be  grave  danger  to  life  in  grasping 
such  an  uninsulated  conductor. 

Thus,  a  person  standing  upon  a  dry  wooden  floor  may  with  safety 
touch  a  bare  wire  through  which  a  current  of  high  voltage  is  pass- 
ing, and  will  in  all  probability  not  be  aware  of  the  fact  that  an  elec- 
tric current  is  flowing  ;  if,  however,  this  person,  while  touching  the 
bare  wire,  should  bring  any  other  part  of  the  body  into  contact 
with  some  other  electric  conductor,  as  a  gas-pipe,  a  water-pipe,  or  a 
grounded  wire,  he  may  receive  an  injurious  and  even  a  fatal  elec- 
tric shock. 

The  quantity  of  current  that,  under  these  circumstances,  will  pass 
through  the  body  depends,  of  course,  not  only  on  the  electromo- 
tive force  of  the  source,  but  also  on  the  resistance  of  the  circuit 
— that  is,  the  body  ;  and  this  resistance  will  be  dependent  upon 
the  nature  of  the  contact  between  the  body  and  the  other  con- 
ductors. It  is,  therefore,  not  possible,  even  with  a  given  electro- 
motive force,  to  say  whether  a  strong  or  a  weak  current  has  passed 
through  the  body,  unless  we  know  whether  good  contact  or  poor 
contact  has  been  made.  As  regards  the  voltage  that  may,  under 
favorable  circumstances,  prove  dangerous,  we  may  say  that  a  con- 
tinuous electromotive  force  of  twenty  volts  cannot  prove  injurious 
when  applied  to  any  part  of  the  uninjured  surface  of  the  body, 
because  from  this  pressure  only  a  small  quantity  of  current  can  thus 
be  obtained. 

Kennelly,  in  experimenting  upon  animals,  has  shown  that  an  al- 


DANGERS  OF  DYNAMO  CURRENTS  l8l 

ternating  electromotive  force  of  fifty  volts  is  capable  of  killing  a  dog 
in  two  or  three  seconds  when  suitably  applied  by  means  of  large 
electrodes  ;  and  from  his  experiments  upon  dogs,  horses,  and  cows 
it  seems  that  with  currents  of 'ordinary  commercial  frequency  the 
danger  from  a  certain  alternating  pressure  is  two  or  three  times  as 
great  as  that  from  the  same  amount  of  continuous  current  pressure. 
The  danger  in  New  York  and  other  large  cities,  with  their  subways 
and  perfected  source  of  supply,  does  not  lie,  as  is  generally 
assumed,  in  the  sudden  increase  of  the  current  strength  or  in  the 
failure  of  supply.  The  actual  dangers  against  which  we  must  guard 
lie,  as  Hedley  has  shown,  in  leakage  currents,  and,  when  the 
alternating  current  is  employed,  also  in  the  breakdown  of  in- 
sulation between  primary  and  secondary  transformers. 

The  first  source  of  danger  has  been  underestimated  or  completely 
ignored  by  all  writers,  with  the  exception  of  Hedley  ;  nevertheless 
the  danger  is  a  menacing  one,  and  may  give  rise  to  serious  accident. 
In  order  to  understand  these  accidents  let  us  see  how  the  direct 
current  is  distributed  to  the  consumer  in  New  York.  This  is  done 
by  the  three-wire  system. 

This  system  consists  of  a  double  circuit,  each  branch  of  which  has 
an  electromotive  force  of  no  volts,  the  entire  circuit  thus  giving 
220  volts.  This  division  is  made  for  purely  practical  purposes, 
inasmuch  as  220  volts  will  carry  a  larger  quantity  of  current  a 
longer  distance  with  a  smaller  percentage  of  loss  than  no  volts 
will. 

In  this  double  circuit  the  middle  or  neutral  wire  leads  to  the 
ground,  or  is,  perhaps,  contrary  to  law,  even  grounded.  The  ac- 
companying diagram  (Fig.  134)  shows  the  wiring  of  such  a  220  volt 
circuit. 

Inasmuch  as  all  water-  and  gas-pipes  are  underground,  the  neu- 
tral or  ground  wire  may  prove  a  source  of  danger  by  carrying  an 
excessive  amount  of  current  into  houses  through  these  gas-  and 
water-pipes,  as  they  actually  form  branches  of  the  neutral  wire  that 
are  free  in  the  rooms  at  all  outlets — i.  <?.,  gas-jets,  chandeliers,  bath- 
tubs, and  faucets.  This  danger  is  shown  in  the  following  diagram 

(Fig-  US)- 

It  will  be  seen  that  the  neutral  wire  G  is  connected,  through  the 


182 


CURRENT    SUPPLY    AND    APPARATUS 


earth,  with  faucets  and  gas  arms,  and  certainly  also  with  waste-pipes. 
Now,  if  the  rheostat  or  current-regulating  device  is  connected 
between  the  one  terminal,  A,  leading  to  the  patient,  and  the  wire  G 
in  the  diagram,  we  can  plainly  see  that  if  the  patient  should  in  any 
way  form  a  ground  connection,  through  a  damp  floor  or  through  a 
bath-tub  with  a  waste-pipe  attached,  or  by  coming  in  contact  with 


220  V 


110 


.to  ground 


110 


220 

FIG.  134. — DIAGRAM  SHOWING  THE  ARRANGEMENT  OF  WIRES  IN  THE  200  VOLT 

CIRCUIT. 


a  gas  arm  or  water  faucet,  the  rheostat  would  become  useless,  as 
the  current  would  take  the  course  of  least  resistance  and  pass  from 
the  ground  through  the  patient  to  the  positive  wire,  thus  giving  the 
patient  the  full  voltage  (i  10  volts)  on  the  line. 

It  is  thus  apparent  that  there  is  danger  connected  with  the  use  of 
the  current  unless  the  right  wires  are  selected  first  and  an  efficient 
controlling  apparatus  put  in  the  proper  place.  The  correct  manner 


THREE-WIRE    SYSTEM 


133 


FIG.  135. — DIAGRAM  SHOWING  THE  DANGER  OF  THE  THREE-WIRE  SYSTEM. 


1 84 


CURRENT    SUPPLY    AND    APPARATUS 


of  introducing  the  controlling  apparatus  is  shown  in  figure  136. 
It  will  here  be  seen  that  the  resistance  is  placed  between  the  main 
branch  of  the  circuit  and  the  patient,  so  that  if  the  patient  come  in 
contact  with  a  grounded  pipe,  the  resistance  will  still  be  between 
him  and  the  source  of  current. 

A  source  of  danger,  which  can,  of  course,  occur  only  with 
transformed  systems,  is  that  due  to  a  breakdown  in  the 
insulation  between  the  primary  and  secondary  windings  of  a 


A 


FIG.  136. — DIAGRAM  SHOWING  WHERE  THE  CONTROLLING  APPARATUS  SHOULD 
BE  PLACED  IN  ORDER  TO  AVOID  DANGER. 


transformer.  As  a  consequence,  the  secondary  windings  would 
have  their  potential  very  materially  raised.  This  is  an  occurrence 
that  cannot  be  guarded  against,  so  the  only  remedy  lies  in  some 
arrangement  by  which  the  current  would  be  cut  off  in  that  event. 
Various  apparatus  for  this  purpose  exist :  In  one  the  secondary 
mains  are  automatically  connected  with  the  earth  upon  a  dangerous 
rise  in  potential ;  in  another  a  second  transformer  is  in  circuit  with 


CONTROL  OF  DYNAMO  CURRENTS 


I85 


the  patient;  or,  finally,  we  may  make  use  of  a  magnetic  cut- 
out in  the  circuit,  so  that  upon  rise  in  the  pressure  of  the  current 
the  cut-out  will  gradually  diminish  the  current  to  zero.  Fusible 
cut-outs  and  lamps  as  safeguards  are  worse  than  use- 
less, for  they  induce  us  to  place  confidence  in  apparatus  that  will 
never  act  promptly,  as  they  require  time  to  melt  or  to  break.  But 
even  the  safety  cut-outs  first  spoken  of,  no  matter  how  well  con- 
structed, must  fail  to  guard  the  patient  against  a  momentary  shock 


.H- 


FIG.  137.— DIAGRAM  SHOWING  How  THE  CURRENT  is  DERIVED  FROM  A  DOUBLE 

SHUNT  CIRCUIT. 

that,  no  matter  how  short  in  duration,  may,  for  all  that  we  know  to 
the  contrary,  do  irreparable  damage. 

No  safety  cut-out  can  act  before  the  increased  current  has  reached 
it,  and  so  soon  as  the  current  has  done  this,  it  has  also  passed  over 
to  the  other  end  of  the  line. 

As  previously  mentioned,  another  source  of  danger  may  lie  in  a 
sudden  increase  of  current  on  the  line  in  consequence  of  an 


1 86  CURRENT    SUPPLY    AND    APPARATUS 

accident  at  the  central  station,  or  through  the  crossing  of  the  supply 
wires  by  wires  from  another  source — e.g.,  arc  lights.  While  this  is 
not  likely  to  happen  in  New  York  city,  a  method  should  be  pro- 
vided to  guard  against  possible  danger  from  such  an  occurrence. 

This  danger  may  practically  be  overcome  by  the  employment  of 
a  compound  shunt.  Here  the  shunted  current  is  again  shunted, 
and  the  already  reduced  voltage  again  reduced.  No  more  delicate 
graduation  of  a  current  can  be  imagined  than  the  one  obtainable  by 
this  means.  A  reference  to  figure  137  will  make  this  clear. 

The  current  is  first  regulated  by  the  resistance  controller  at  B. 
If  the  full  resistance  be  interposed,  all  the  current  will  pass  through 
the  shunt,  and  the  quantity  of  current  in  the  shunt  circuit  is  propor- 
tional to  the  interposed  resistance.  Now,  following  the  shunt  cir- 
cuit to  C,  the  process  is  repeated  by  shunting  the  current  again  and 
placing  another  resistance  controller  in  one  arm  of  the  shunt,  so 
that  the  ultimate  current  is  the  result  of  a  double  shunt.  I  believe 
that  this  is  the  first  time  that  this  idea  has  been  practically  applied. 

How  to  Use  the  Central  Station  Currents. — We  are  now  in 
a  position  to  use  any  current  at  our  disposal  for  any  purpose  that 
may  be  desired. 

It  is  simply  a  question  of  a  suitable  device  for  controlling  the 
current  for  the  purpose  in  question,  and  of  placing  this  device  at  the 
proper  location  in  the  circuit. 

The  device  for  controlling  the  direct  current  from  the  main  will 
differ  from  that  necessary  to  control  the  battery  current  only  in  its 
adaptation  to  the  larger  volume  of  current  that  we  make  use  of. 
The  principles  governing  such  adaptations  are  as  follow : 

i.  In  galvanization  of  the  human  body  no  more  than  one  am- 
pere of  current  is  needed;  therefore  additional  resistance  sufficient 
to  limit  the  volume  to  this  amount  should  be  placed  and  allowed  to 
remain  in  series  with  the  controlling  device.  This  is  the  limit 
resistance  and  is  non variable.  As  such  a  limit  resistance,  incan- 
descent lamps  have  been  used,  the  lamps  limiting  the  current  in 
accordance  with  their  candle-power ;  thus,  with  a  1 10  volt  current 
an  8  candle-power  lamp  would  limit  the  current  to  ^  of  an 
ampere ;  a  16  candle-power  lamp  would  limit  the  current  to  ^  of  an 


CONTROL  OF  DYNAMO  CURRENTS  l8/ 

ampere;  a  32  candle-power  lamp  would  limit  the  current  to  i 
ampere  ;  a  50  candle-power  lamp  would  limit  the  current  to  I  ^ 
amperes  ;  but  these  limits  are  only  correct  when  these  lamps  are 
at  full  incandescence,  as  the  carbon  filaments  have  a  great  deal 
higher  resistance  when  below  incandescence.  On  the  other  hand, 
the  life  of  the  lamp  is  limited  and  the  filament  is  apt  to  break,  or  may 
become  detached  from  its  socket,  even  before  it  is  exhausted,  by  a 
sudden  jar,  and  thus  the  supply  of  current  may  suddenly  be  cut  off. 

A  wire  resistance  of  the  necessary  capacity  has  very  many 
advantages  :  it  furnishes  a  trustworthy  and  invariable  resistance  ; 
it  will  not  deteriorate,  and,  if  properly  arranged,  it  will  not  get  out 
of  order. 

2.  We  must,  further,  make  use  of  some  contrivance  for  regu- 
lating the  intensity  and  the  quantity  of  the  current  thus 
obtained. 

In  all  contrivances  now  in  use,  together  with  a  galvanic  con- 
troller (rheostat),  lamps  are  employed  for  shunting  off  current — 
that  is,  for  reducing  the  voltage  or  intensity.  Nothing  can  be 
more  reprehensible  than  an  arrangement  of  this  kind,  for  should 
such  a  shunt  lamp  break  down  or  loosen  from  its  socket,  the  volt- 
age passing  through  the  patient  would  suddenly  and  veiy  materi- 
ally be  augmented. 

For  affecting  the  relative  intensity  of  a  current  a  rheo- 
stat of  considerably  higher  resistance  is  connected  in  series  with 
the  limit  resistance,  and  from  this  rheostat  we  derive  our  current, 
properly  modified  and  perfectly  adjustable. 

In  the  construction  of  rheostats  for  use  with  the  street  current 
we  must  not  fail  to  consider  that  a  greater  quantity  of  heat  is  apt 
to  be  generated  in  the  resistance  cylinders  than  would  be  the  case 
if  the  battery  current  were  used. 

This  heat-production  must,  if  possible,  be  guarded  against,  not 
only  because  it  may  be  so  great  as  to  fuse  the  wires,  and  thus 
destroy  the  apparatus,  but  also  because  the  resistance  in  the  con- 
trolling device  will  vary  with  the  temperature  and  thus  interfere 
with  accurate  measurements.  This  is  the  main  reason  why  carbon 
rheostats  are  more  or  less  unsatisfactory  when  used  in  connection 
with  the  street  current. 


1 88  CURRENT    SUPPLY    AND    APPARATUS. 

The  only  satisfactory  rheostat  for  use  in  connection  with  the 
street  current  is  a  metal  resistance  device  of  proper  capac- 
ity, with  sufficient  heat-radiating  surface. 1 

The  method  that  I  employ  for  the  regulation  of  the  current 
(voltage  and  amperage)  from  the  main  is,  therefore,  as  follows  : 

A  limit  resistance  made  in  accordance  with  the  foregoing  prin- 
ciples is  inserted  at  the  point  of  entrance. 

A  resistance  cylinder  is  placed  in  the  main  circuit,  from 
which  the  current  is  shunted. 

This  shunt  current  is  passed  through  another  controller, 
and  herefrom  is  derived  another  current;  and  in  this  circuit  the 
patient  is  placed. 

The  current  in  the  shunt  circuit  will  always  be  dependent  upon 
the  proportionate  resistances  of  the  main  circuit  and  of  the  shunt 
circuit ;  the  current  following  the  path  of  least  resistance.  In  the 
resistance  apparatus  in  the  main  circuit  (first  volt  controller) 
two  terminals  or  slide  contacts  are  employed,  for  the  purpose  of 
varying  the  relative  resistances  according  to  their  position  upon  the 
cylinder.  If  the  terminals  are  at  opposite  ends  of  the  resistance 
cylinder,  the  entire  resistance  is  interposed  in  the  main  circuit,  and 
the  maximum  amount  of  current  obtainable  will  flow  through  the 
shunt  circuit.  As  the  contacts  are  approached  to  each  other,  the 
interposed  resistance  in  the  main  circuit  grows  less  and  the  current 
in  the  shunt  circuit  becomes  correspondingly  diminished,  until  they 

1  Heating  capacity  :  Iio  volts  will  send  }4  an  ampere  through  220  ohms ;  if  this  re- 
sistance be  made  to  consist  of  a  thin  wire  about  four  feet  in  length,  it  would  at  once 
become  red-hot  when  connected  with  a  no  volt  circuit ;  if  the  wire  were  made  longer, 
it  would  necessarily  have  to  be  made  thicker  in  order  to  keep  its  resistance  at  220  ohms  ; 
then,  while  the  same  quantity  of  heat  would  actually  be  generated  in  the  wire,  it  would, 
nevertheless,  not  become  so  hot  as  in  the  case  of  the  thinner  wire,  because  it  presents  a 
larger  surface  to  the  surrounding  atmosphere,  and  thus  permits  of  the  escape  of  more 
heat.  Therefore  the  greater  the  heat-radiating  surface,  the  less  heat  will  be  generated 
throughout  the  entire  resistance.  If,  however,  we  take  the  thicker  wire,  and,  instead 
of  connecting  it  to  a  no  volt  circuit  connect  it  to  one  of  220  volts,  we  should  again 
have  the  same  state  of  affairs.  It  is  thus  apparent  that  our  resistance  must,  in  addition 
to- having  ample  heat-radiating  surface,  also  be  adjusted  in  accordance  with  the  pressure 
of  the  available  source,  and  the  resistance  body  selected  must  be  of  sufficient  capacity 
to  carry  the  limit  of  current  required  for  the  special  purpose. 


DOUBLE  SHUNT  CURRENT  189 

are  directly  opposite  to  each  other  on  the  cylinder,  when  no  cur- 
rent will  flow  in  the  shunt.  The  electromotive  force  of  the  shunt 
current  will  also  depend  on  the  resistance  in  the  main  circuit,  as 
already  elucidated. 

Owing  to  the  construction  of  the  resistance  cylinder,  the  variations 
in  the  intensity  of  the  shunt  current  take  place  very  gradually  by 
small  fractions  of  a  volt. 

The  shunt  current  then  selected  is  still  further  reduced  by>  the 
second  controller,  which  is  constructed  similarly  to  controller 
No.  I,  only  that  it  is  so  modified  that  no  switch  is  required  to  turn, 
the  current  on  and  off  The  same  movement  (hand  or  motor 
power)  that  actuates  the  slide  contacts  turns  the  current  on  and  off 
by  means  of  two  bars  and  a  spring  that  traverses  them.  These 
circuit-breaking  bars  run  parallel  with  one  of  the  slide  bars,  and 
each  one  forms  a  continuous  conductor  from  one  end  of  the  resis- 
tance cylinder  to  the  other  ;  but  at  that  point  at  which  the  two  slide 
contacts  are  directly  opposite  to  each  other,  the  spring,  which  has 
formed  an  electric  connection  between  the  two  bars,  is  forced  to 
ride  into  an  insulation,  thus  breaking  the  electric  contact  between 
the  two  circuit-breaking  bars  ;  then  no  current  will  pass  through  the 
controller. 

The  current  in  the  shunt  cannot  be  shut  off  with- 
out gradually  diminishing  it  to  zero. 


CHAPTER   IV 

APPARATUS  FOR  ALTERING  ELECTROMOTIVE 

FORCE 

Induced  or  Faradaic  Currents.  Magneto-electric  Machines.  Volta-mag- 
netic  Machines.  Dubois-Reymond  Coils.  Faradimeter .  Standard  Coils. 
Current  Source.  Sinusoidal  Currents  and  Apparatus.  Apparatus  for 
High  Frequency  Currents.  Hydro-electric  Baths.  Cautery  Apparatus. 
Transformer.  Commutator.  Storage  Cells.  Exploring  Lamps. 

Mechanical  Induction  Apparatus. 

The  first  induction  machines  used  in  medicine  were  magneto- 
electric  or  rotary  apparatus.  These  machines  were  used  for  a 
long  time,  but  were  finally  entirely  displaced  by  the  volt  a-  or 
electro-magnetic  apparatus.  Without  going  into  the  history 
of  these  machines  or  describing  them  in  detail,  an  illustration  may 


FIG.  138. — MAGNETO-ELECTRIC  MACHINE. 

be  given,  so  that  the  student  shall  not  be  entirely  unfamiliar  with 
their  appearance.     (See  Fig.  138.) 

The  advantages  of  such  machines  are  that  they  always,  without 
special  preparation,  furnish  a  current  that,  with  equable  rotation, 
possesses  one  and  the  same  intensity ;  they  are  durable ;  the  cost 

190 


DYNAMIC    INDUCTION    APPARATUS  19! 

of  maintenance  is  reduced  to  a  minimum,  and  they  may  be  used  for 
the  production  of  unidirectional  or  of  alternating  currents. 

In  order,  however,  to  accomplish  all  this,  the  machine  must  be 
complicated  in  its  construction,  and  must  be  made  so  large  that  its 
portability  is  sacrificed.  Furthermore,  an  assistant  is  necessary  to 
rotate  the  coils  or  magnet,  and  the  regularity  of  such  rotation  leaves 
much  to  be  desired.  With  irregularity  of  rotation  current  fluctua- 
tions are  unavoidable.  The  use  of  a  motor  for  purposes  of  rotation 
is  complicated  and  impracticable.  For  these  reasons  and  because 
the  volta-induction  apparatus  works  automatically,  admits  of  modifi- 
cation of  the  current  intensity  and  of  the  current  interruptions,  is  per- 
fectly portable,  and  is  very  much  cheaper,  it  has,  for  all  practical 
medical  use,  displaced  the  old  magneto-electric  machines. 

Volta-induction  Apparatus. 

The  volta-induction  apparatus  manufactured  for  medical  pur- 
poses vary  considerably  in  shape  and  appearance,  but  the  principles 
of  construction  remain  the  same.  These  principles  are  : 

1.  The  primary  coil,  the  function  of  which  is  to  furnish  a  path 
for  the  battery  current  and  to  interrupt  and  transform  that  current 
in  such  a  manner  as  to  create  induced  currents  in  a  secondary  coil 
near  by,  need  be  made  of  but  few  turns  of  comparatively  coarse 
wire.      For  the  purpose  of  giving  a  different  quality  to  the  primary 
current  the  number  of  turns  may  be  increased.     This  primary  coil 
surrounds 

2.  The  temporary  magnet,  which  consists  of  a  soft-iron  bar  or 
a  bundle  of  soft-iron  wires,  and  becomes   magnetized  when   the 
battery  current  flows  through   the  primary  coil,  again  losing  its 
magnetism   when    this    current  is    interrupted.      This    magnet,   in 
addition  to  augmenting  the  inductive  action,  may  also  be  made 
use  of  to  interrupt  the  current  automatically  through  the  aid  of 

3.  The   Circuit   Breaker  or   Interrupter. — The  current  that 
flows   through   the  primary  coil   around  the   wire  core   must  be 
broken  at  intervals  in  order  to  effect  the  change  of  electromotive 
force  necessary  to  the  creation  of  induced  currents.      Such  inter- 
ruptions are  produced  in  the  ordinary  coils  by  means  of  a  spring, 
one  end  of  which  is  fastened  to  the  base  of  the  apparatus,  the  other 


192 


APPARATUS  FOR  ALTERING  ELECTROMOTIVE  FORCE 


end  being  free  directly  on  a  line  with  the  wire  core,  and  having  an 
iron  head  attached  to  it.  The  tension  of  the  spring  is  regulated  by 
means  of  a  set-screw.  This  interrupter,  with  its  connections,  is 
shown  in  figure  139. 

The  current  passing  through  the  primary  coil,  P,  magnetizes  the 


'/MHW//////I.  •W/l/HHIHtM/M/li. 


FIG.  139. — SHOWING  CIRCUIT  BREAKER  AND  ITS  CONNECTIONS. 

iron  core,  C ;  by  its  magnetic  force  it  attracts  the  head  on  the  in- 
terrupter, I,  and  draws  the  spring  away  from  the  adjusting  screw, 
S,  thus  interrupting  the  current.  As  soon  as  the  current  is  inter- 
rupted the  iron  core  loses  its  magnetism  and  releases  the  spring, 


FIG.   140. — THE  NEEF  OR  WAGNER  HAMMER. 

which  flies  back  and  again  comes  in  contact  with  the  set-screw,  thus 
recompleting  the  circuit. 

In  many  induction  coils  the  interruptions  are  effected  by  means 
of  a  Neef  or  Wagner  hammer  (Fig.  140).  Here  a  special  electro- 
magnet is  employed. 


ELECTROMAGNETIC    INDUCTION    APPARATUS  193 

When  the  spring  in  either  form  is  in  action,  small  sparks  will  be 
seen  to  pass  between  the  spring  and  the  adjusting  screw.  Hereby 
small  particles  of  metal  are  torn  off  from  both  plate  and  screw 
point,  which  in  time  become  markedly  worn.  In  order  to  prevent 
this  wear  and  tear  as  much  as  possible  the  screw  point  and  plate 
are  made  of  platinum.  Hereby,  also,  the  oxidation  of  these  parts 
is,  to  a  certain  extent,  prevented.  The  rapidity  with  which  the  cur- 
rent can  be  interrupted  by  means  of  this  mechanism  varies  greatly 
in  different  instances,  depending  upon  the  length  of  the  spring,  its 
elasticity,  etc.  ;  each  such  spring  can,  however,  be  regulated  within 
certain  limits,  so  that  the  interruptions  become  slower  or  more 
rapid.  The  sooner  the  spring  meets  the  screw  point  again  after 
having  been  drawn  away  from  it  by  the  electromagnet,  the  more 
rapid  will  be  the  vibrations ;  therefore  the  further  we  screw  the 
point  down,  without,  however,  screwing  it  so  tightly  that  the  spring 
is  prevented  from  vibrating,  the  more  interruptions  will  we  have  ; 
and  the  further  the  point  is  screwed  back,  yet  allowing  the  spring  to 
make  good  contact,  the  fewer  interruptions  will  we  obtain.  The 
interruptions  may  be  varied  still  more,  as  regards  their  relative  slow- 
ness, by  lengthening  the  spring,  through  the  attachment  of  a  rod 
upon  which  a  metal  ball  can  be  raised  and  lowered,  or  by  means 
of  a  rod  and  ring,  as  in  Flemming's  apparatus.  For  special  work 
the  interruptions  may  be  effected  by  means  of  clockwork,  or 
Engelmann's  segmentary  rotary  interrupter,  run  by  an  electric 
motor,  may  be  employed.  Thus  great  variations  and  regularity 
of  interruptions  are  obtained  ;  but  for  all  practical  purposes  the 
simple  Wagner  hammer  will  answer. 

4.  The  secondary  coil,  or  the  induction  coil  proper, 
must  be  made  of  finer  wire  than  is  used  for  the  primary  coil, 
have  a  greater  number  of  windings,  and  the  length  of  wire  be 
proportionately  increased.  The  increased  length  of  wire  neces- 
sitates an  increased  number  of  turns  in  each  layer.  The  lines 
of  magnetic  force  emanating  from  the  primary  coil  and  tem- 
porary magnet  are  increased  proportionately  to  each  extra  turn, 
and  are  cut  by  the  secondary  coil.  In  consequence  of  this  a 
greater  number  of  windings  is  deemed  advantageous  by  some. 
But  this  advantage,  derived  from  the  increased  length  and  num- 
13 


i94 


APPARATUS  FOR  ALTERING  ELECTROMOTIVE  FORCE 


her  of  turns  of  wire  of  the  secondary  coil,  has  its  limit.  The 
primary  battery  may  not  be  able  to  overcome  the  increased 
resistance,  and,  in  addition,  a  self-induction  current  is  set  up, 
thus  materially  reducing  the  secondary  induced  current.  The 
efficiency  of  the  faradaic  apparatus  depends  greatly  on  the  nature  of 
the  current  derived  from  the  secondary  coil,  and  at  times  different 
forms  of  current  are  required  for  various  therapeutic  purposes.  To 
meet  this  need  the  manufacturers  of  apparatus  have  arranged  various 
devices.  Some  furnish  a  series  of  coils  wound  with  graduated  turns 
and  thicknesses  of  wire.  Others  use  a  very  long  wire,  of  uniform 
thickness,  with  many  turns,  and  tap  the  wire  at  regular  intervals  by 
means  of  a  switch  ;  thus  required  portions  or  even  the  whole  coil 
can  be  thrown  in. 

This  secondary  coil  may  be  fixed,  or  may  be  movable  along  a 


FlG.    141. — DUBOIS-REYMOND   COIL. 

track,  sliding  over  and  covering  or  uncovering  the  primary  coil  to 
any  desired  extent.  If  the  coil  slides,  the  track  along  which  the 
secondary  coil  moves  should  be  graduated  with  a  millimeter  scale, 
in  order  to  show  the  extent  of  primary  coil  and  core  that  at  each 
move  of  the  secondary  coil  still  remains  covered  by  it.  Such  an 
apparatus  is  shown  in  figure  141,  and  is  known  as  a  Dubois- 
Reymond  coil.  Upon  the  horizontal  base  S,  which  forms  the 
track  for  the  secondary  coil,  is  fastened  the  horizontal  millimeter 
scale  and  the  vertical  head-board  G,  which  carries  the  primary  coil  /, 
the  binding  posts  c  d  for  the  extra  current,  as  well  as  supporters 
for  the  interrupter.  Upon  the  track  itself  is  mounted  a  secondary 
coil,  //,  which  is  movable  over  the  primary  coil ;  the  latter  having 
in  its  interior  the  iron  core,  ///,  made  up  of  bundles  of  wire. 

In  addition  hereto  we  see  upon  the  head-end  two  binding  posts, 


DUBOIS-REYMOND    COIL  1 95 

a,  b,  for  the  battery  connection,  and  at  the  foot  of  the  secondary 
coil  two  binding  posts,  etf,  for  the  secondary  current.  If  the  poles 
of  the  current  source  are  respectively  connected  with  a  and  b,  the 
current  flows  first  through  the  automatic  interrupter,  which  is 
thereby  set  into  action,  and  then  through  the  wires  of  the  primary 
coil.  The  extra  current  may  be  obtained  by  connecting  the  elec- 
trodes with  c  and  d,  while  the  secondary  current  is  obtained  by 
connecting  them  with  e  and/! 

The  strength  of  a  current  from  an  induction  apparatus  may  be 
controlled  in  a  variety  of  ways,  by  regulating  the  strength  of  either 
the  primary  or  the  secondary  current.  In  the  forms  of  apparatus 
in  which  the  secondary  coil  is  fixed,  the  strength  of  the  current 
is  regulated  by  means  of  a  movable  iron  core  or  by  means 
of  a  damper.  In  the  first  case  the  core  of  soft-iron  wires 
around  which  the  primary  coil  flows  may  be  pulled  out  or  pushed 
in.  The  primary  current  is  weakest  if  the  core  is  drawn  out,  and 
becomes  proportionately  stronger  the  further  the  core  is  pushed  in. 
In  the  second  case  the  electromotive  force  is  altered  by  sliding  a 
brass  or  copper  tube  over  the  fixed  wire  core,  thus  cutting  off  the 
inducing  effect  of  the  core  entirely  when  it  is  completely  covered, 
and  increasing  it  as  the  damper  is  drawn  out — /.  e.,  the  core  un- 
covered. 

In  the  apparatus  of  the  Dubois-Reymond  type  the  current  strength 
is  regulated  by  varying  the  extent  to  which  the  secondary  coil 
covers  the  primary  one,  in  the  manner  already  described.  For  all 
diagnostic  purposes  this  method  of  current  regulation  is  the  one 
that  should  be  chosen. 

Measurement  of  Induction  Coil  Currents. 

The  arguments  advanced  in  support  of  the  use  of  instruments  of 
precision  in  the  employment  of  the  voltaic  current  for  medical  pur- 
poses apply  with  equal  force  to  the  induced  currents.  While  the 
quantity  of  any  direct  or  uninterrupted  current  flowing  at  a  given 
time  can  be  measured  satisfactorily  by  means  of  a  galvanometer 
introduced  into  the  circuit,  no  instrument  has  as  yet  been  devised 
that  is  capable  of  doing  this  for  induction  coil  currents.  The 
induced  current  that  arises  in  the  primary  coil  being  a  current  of 


196      APPARATUS  FOR  ALTERING  ELECTROMOTIVE  FORCE 

one  direction,  may,  by  means  of  a  very  delicate  galvanometer,  be 
measured  approximately,  but  the  current  flow  is,  on  account  of  the 
interruptions,  of  so  short  duration  that  the  needle  cannot  come  to 
rest,  and  no  actual  reading  of  the  galvanometer  scale  can  therefore 
be  made.  The  secondary  current  is  alternating  as  well  as  inter- 
rupted, and  no  alternating  meter  exists  that  will  register  the  small 
currents  of  the  secondary  coil. 

As  the  chief  effects  of  an  induced  current  depend  upon  the  quan- 
tity and  electromotive  force  of  the  current,  we  must  demand  of  any 
serviceable  meter  that  it  record  either  the  quantity  of  current  in  the 
circuit  or  the  voltage  of  the  current.  This  is  being  done  in  a  crude 
and  unsatisfactory  manner  by  the  millimeter  scale,  which  indicates 
the  relative  position  of  the  coils.  Inasmuch  as  the  strength  of  the 
induced  current  depends  upon  the  strength  of  the  inducing  current, 
upon  the  number  of  turns  and  size  of  the  wire  used  in  the  coils,  and 
upon  the  size  and  shape  of  the  temporary  magnet,  it  will  readily  be 
seen  that  any  scale  can  serve  only  as  an  approximate  index  to  the 
strength  of  current  in  the  individual  apparatus  for  which  it  is  con- 
stituted, and  even  then  must  entirely  disregard  the  variations  of  the 
strength  of  the  primary  and  secondary  currents,  due  to  variations 
in  the  strength  of  the  current  from  the  exciting  source. 

Von  Ziemssen  and  Edelmann  have  attempted  to  correct  the 
fault  due  to  variations  in  the  inducing  current  by  introducing  an 
adjustable  resistance  in  circuit  with  the  primary  coil,  thus 
affording  a  means  by  which  the  resistance  in  the  primary  coil  may 
be  altered  in  accordance  with  the  variations  in  strength  of  the  cur- 
rent from  the  primary  source,  and  the  strength  of  the  inducing  cur- 
rent be  kept  constant. 

In  the  Edelmann  faradimeter,  as  this  instrument  is  called,  the 
inducing  current  is  kept  constant  at  300  milliamperes. 

With  the  inducing  current  constant,  the  inducing  effect  upon  the 
magnet  and  secondary  winding  will  correspondingly  be  constant. 
The  scale  that  accompanies  the  instrument  is  graduated  in  volts, 
from  5  to  200,  and  so  long  as  the  strength  of  the  inducting  current 
is  exactly  300  milliamperes,  the  number  of  volts  marked  on  this 
scale,  along  which  the  secondary  coil  slides,  is  correct.  In  theory 
this  instrument  is  perfectly  trustworthy  so  long  as  there  is  a  fixed 


MEASUREMENT    OF    FARADAIC    CURRENTS  1 97 

resistance  between  the  terminals  of  the  secondary  coil ;  but  in  prac- 
tice this  resistance,  whether  in  diagnostic  or  therapeutic  applications, 
is  constantly  varying,  so  that  the  actual  voltage  in  the  circuit  will 
rarely  correspond  with  the  figures  indicated  upon  the  scale. 

Even  admitting  that  the  method  is  practical  for  scientific  use,  it  re- 
quires not  only  a  specially  constructed  induction  coil,  but  also  special 
measuring  apparatus ;  these  facts  will  act  as  an  obstacle  to  its  general 
use  for  therapeutic  purposes.  Nevertheless,  some  system  of  uniform- 
ity in  the  construction  of  coils  should  be  observed  ;  for  at  present,  on 
account  of  the  varied  dimensions  given  to  coils  by  different  makers, 
even  with  the  specification  of  the  kind  of  cell  employed  as  well  as 
the  distance  between  the  primary  and  secondary  coils,  the  current 
from  one  apparatus  cannot  be  compared  with  that  furnished  by 
another.  Thus  the  results  obtained  diagnostically  or  therapeutic- 
ally  by  one  observer  cannot  be  tested  accurately  by  others.  At  the 
general  meeting  of  the  International  Electrical  Congress,  held  in 
Paris  on  September  28,  1881,  it  was  resolved  that  the  simple  state- 
ment of  the  distance  between  the  primary  and  secondary  coils  of 
a  Dubois-Reymond  sled  apparatus  suffices  for  the  determination 
of  the  induced  currents  used  in  electrotherapy,  provided  that  in  its 
construction  an  apparatus  of  standard  dimensions  be  used  as  a 
model,  and  that  one  and  the  same  kind  of  cell  be  used  as  current 
source.  The  normal  apparatus  recommended  possesses  the  follow- 
ing dimensions  : 

Primary  Coil.  Secondary  Coil. 

Length  of  coil,      88  mm.  65    mm. 

Diameter  of  coil, 36    "  68       " 

Diameter  of  wire, I     "  0.25" 

Number  of  turns  of  wire, 300  5000 

Number  of  layers  of  wire, 44  28 

Resistance,  about 1.5  ohm  300  ohms. 

The  current  for  working  an  induction  apparatus  must,  if  cells 
be  used,  be  obtained  from  cells  having  a  low  internal  resistance  and 
as  high  an  electromotive  force  as  possible.  The  best  cell  for  this 
purpose  would  be  the  Grenet,  but  on  account  of  the  trouble 
attendant  upon  frequent  recharging  and  the  necessity  of  immersing 
and  removing  the  zinc  each  time  before  and  after  using  the  appa- 
ratus, other  cells  are  practically  more  convenient. 


198      APPARATUS  FOR  ALTERING  ELECTROMOTIVE  FORCE 

For  nonportable  apparatus,  those  that  form  part  of  the  sta- 
tionary office  outfit,  large  Leclanche  cells  are  most  desirable. 
For  portable  induction  coils  adry  Leclanche  cell  will  be  found 
eminently  satisfactory.  For  experimental  purposes  the  greatest 
constancy  of  the  inducing  current  can  be  obtained  by  the  use  of 
thermopiles.  They  are  started  by  lighting  a  small  gas,  oil,  or 
spirit  flame.  Their  convenience,  reliability,  and  durability  leaves 
little  to  be  desired.  The  direct  current  from  the  central  station 
may  likewise  be  used,  and  will  be  found  unobjectionable. 

In  order  not  to  burn  the  platinum  contact  plate  on  the  interrupter 
of  the  ordinary  faradaic  coil,  it  is  necessary  to  reduce  the  pressure 
of  the  direct  current  to  that  which  would  be  obtained  from  two  or 
three  cells — i.  e.,  four  volts. 

A  rheostat,  as  already  described,  may  be  used  for  this  purpose, 
but  it  is  unnecessary  to  limit  to  I  ^  ampere,  or  to  go  so  high 
as  twenty-three  volts.  In  fact,  all  that  would  be  required  for  operat- 
ing the  coil  would  be  a  lamp  of  thirty-two  candle-power  in  series 
with  a  four  to  six  ohm  resistance  wire  of  one  ampere  capacity. 
This  would  make  it  equal  to  a  three  or  four  cell  battery,  because  a 
shunt  or  parallel  connection  with  six  ohms  carrying  one  ampere 
yields  about  six  volts  at  one  ampere — i.  e.y  IIOX^,  or  5.6.  volts.  If 
desirable,  this  could  be  still  further  regulated. 

Sinusoidal  Apparatus. 

It  is  not  at  all  easy  to  construct  a  machine  that  will  generate  a 
true  sinusoidal  current,  on  account  of  the  difficulty  of  producing 
a  magnetic  field  that  will  not  vary  while  an  armature  containing  iron 
is  revolved  in  it.  As  previously  stated,  the  magneto-electric 
machine  generates  a  current  approximately  sinusoidal  in  character. 

Dr.  J.  H.  Kellogg,  of  Battle  Creek,  Mich.,  has  for  a  number  of 
years  used  a  common  magneto-generator,  wound  for  about  fifty 
volts  at  3000  revolutions,  as  a  source  of  sinusoidal  currents.  A 
magneto-generator  can  be  made  to  give  a  current  that  is  more 
nearly  sinusoidal  than  is  that  obtained  from  the  ordinary  machine, 
by  properly  shaping  the  pole  pieces  and  armature.  In  his  machine 
(Fig.  142)  Dr.  Kellogg  has  not  only  done  this,  but  has  replaced 
the  permanent  magnet  by  a  separately  excited  electromagnet,  thus 


SINUSOIDAL    CURRENTS 


199 


permitting  of  a  variation  of  the  electromotive  force  generated  with- 
out varying  the  speed  of  the  armature. 

Mr.  A.  E.  Kennelly  has  designed  an  alternator  for  electrothera- 
peutic  purposes,  shown  in  figure   143,  in  which  the  principle  of 


FIG.  142. — MAGNETO-GENERATOR  FOR  DEVELOPING  A  SINUSOIDAL  CURRENT. 


FIG.  143. — AN  ALTERNATOR  FOR  GENERATING  A  CURRENT  OF  THE  SINUSOIDAL 

TYPE. 

magneto-electric  induction  is  applied  in  a  different  manner.  This 
machine,  which  in  my  experience  is  the  most  satisfactory  small 
alternator  obtainable,  consists  of  12  coils,  C,  C,  C,  C,  on  the  field 
frame,  wound  with  two  circuits,  one  of  coarse  wire,  excited  by  a 


2OO      APPARATUS  FOR  ALTERING  ELECTROMOTIVE  FORCE 

continuous  current  from  a  pair  of  binding  posts,  P,  and  a  fine  wire 
circuit  connecting  with  the  binding  posts  S.  The  armature  A,  A, 
which  is  rotated  by  a  small  pulley  at  one  end  of  the  shaft,  is  con- 
structed of  sheets  of  soft  iron  and  carries  teeth,  T,  T,  in  such  a 
manner  as  alternately  to  open  and  close  the  magnetic  circuits  of  the 
coils  C,  C,  C,  C.  Each  revolution  of  the  armature  produces  twelve 
complete  periods,  or  twenty -four  alternations.  As  soon  as  the 
teeth  bridge  across  adjacent  poles,  magnetic  flux  is  poured  through 
the  secondary  or  fine  wire  circuits,  inducing  in  them  an  electromo- 
tive force  in  one  direction,  and  as  soon  as  the  teeth  pass  beyond 
this  position,  the  magnetic  circuits  are  open  and  the  secondary  coils 
emptied  of  flux,  thus  inducing  an  oppositely  directed  electromotive 
force. 

This  alternator  furnishes  an  alternating  current  of  approximately 
sinusoidal  type,  whose  alternations  are,  within  certain  limits,  under 
control,  according  to  the  speed  with  which  it  is  driven.  The  elec- 
tromotive force  obtainable  from  such  a  machine  is  about  fifty  volts. 

The  electromotive  force  of  the  secondary  circuit  depends  upon 
the  strength  of  the  inducing  or  primary  current,  and  this  may 
be  varied,  independently  of  the  frequency,  by  means  of  a  rheostat 
placed  in  this  primary  circuit.  This  circuit  may  be  derived  from 
primary  batteries  or  from  central  stations,  and  should  have  a 
capacity  of  two  amperes. 

Apparatus  for  High  Frequency  Currents. 

The  simplest  arrangement  for  obtaining  alternating  currents 
of  high  frequency  for  medical  purposes  is  that  described  by  d'Ar- 
sonval.  He  makes  use  of  a  condenser  connected  with  a  power- 
ful induction  coil  (a  Ruhmkorff  coil),  capable  of  giving  a  spark 
of  from  15  to  25  centimeters,  and  conducts  the  current  from  such  a 
coil  into  the  inner  armatures  of  two  Leyden  jars.  The  external  ar- 
matures of  these  jars  are  connected  by  means  of  a  solenoid  of  thick 
wire.  (See  Fig.  144.) 

When  the  ends  of  the  conductors  attached  to  the  internal  arma- 
tures of  the  jars  are  approached  near  to  each  other,  a  discharge  of 
sparks  takes  place,  and  the  solenoid  is  traversed  by  an  alternating 
current  of  high  frequency,  which  may  be  utilized  by  the  attachment 


SOLENOID    FOR    HIGH    FREQUENCY    CURRENTS 


201 


of  conductors  to  this  solenoid  ;  the  current  thus  obtained  will  be 
increased  proportionally  as  the  number  of  turns  of  the  solenoid 
comprised  between  these  conductors  is  increased.  If  it  is  desir- 
able still  further  to  augment  the  electromotive  force,  the  solenoid 
of  thick  wire  may  be  made  to  act  upon  another  solenoid  of  fine 
wire. 

The  Ruhmkorff  coils  are  usually  so  constructed  as  to  be  worked 
by  a  current  from  a  primary  or  a  secondary  battery  ;  if  the  1 10  volt 
electric-light  current  is  to  be  used  for  this  purpose,  special  modifi- 
cations of  the  coil  become  necessary.  The  solenoid  may  be  of 


FIG.  144. — APPARATUS  FOR  OBTAINING  A  HIGH  FREQUENCY  CURRENT. 

various  sizes — even  so  large  that  the  entire  body  of  the  patient  may 
be  incased  by  it. 

These  high  frequency  currents,  caused  by  the  oscillations  of  a 
charge  in  a  solenoid,  may  be  made  to  act  upon  a  subject  in  three 
different  ways  : 

1.  By  shunting  the  current  through  the  body  of  the  patient. 
The  patient  is  connected  in  a  shunt  circuit  with  any  two  points  of 
the  solenoid,  and  the  current  is  applied  to  the  body  by  means  of 
electrodes  similar  to  those  used  in  galvanization  and  faradization. 

2.  By  autoconduction. — The  patient  or  the  part  to  be  acted 
upon  is  placed  inside  of  the  solenoid,  without  having  any  direct 
connection  with  any  part  of  the  circuit. 


2O2      APPARATUS  FOR  ALTERING  ELECTROMOTIVE  FORCE 

3.  By  condensation. — The  patient,  connected  to  one  point  of 
the  solenoid,  forms  an  armature  of  a  condenser,  the  second  arma- 
ture being  connected  at  another  point  or  being  made  up  of  the  re- 
mainder of  the  solenoid  (unipolar  application). 

Apparatus  for  Hydro-electric  Baths. 

Galvanic  and  faradaic  currents  may  also  be  conducted  to  the 
human  body  by  means  of  a  bath.  The  patient  is  immersed  in 
water,  to  a  greater  or  less  extent,  and  the  water,  which  is  in  direct 
contact  with  the  body,  constitutes  the  electrode  by  which  the  cur- 
rent is  applied.  Two  methods  of  arranging  such  baths  must  be  dif- 
ferentiated, the  monopolar  and  the  dipolar. 

In  a  monopolar  bath  the  wall  of  the  metal  tub  is  utilized  as  a 
large  electrode.  The  current  entering  here  is  conducted  to  the 
entire  surface  of  the  body  that  is  in  contact  with  the  water,  and 
passes  out  by  means  of  an  iron  bar  covered  with  wet  chamois  skin, 
which  is  grasped  in  the  hands.  The  metal  tub  should  have  a  per- 
forated wooden  lining,  so  that  the  body  of  the  patient  will  not 
directly  touch  the  metal.  Better  still  would  be  the  use  of  a  wooden 
tub,  with  a  large  plate  electrode  entering  it.  There  is,  however, 
one  objection  attached  to  this  form  of  bath,  no  matter  of  what 
material  the  tub  is  made — namely,  that  the  grasping  of  the  metal 
bar  concentrates  so  much  of  the  current  upon  the  hands  that  a  severe 
contraction  of  all  the  muscles  of  the  hands  and  arms  takes  place, 
while  the  current  that  is  spread  over  the  remainder  of  the  body  is 
hardly  perceived.  The  metal  bar,  therefore,  should  be  discarded,  and 
in  its  stead  a  large  metal  electrode  of  about  400  square  centimeters 
surface,  whose  edges  are  covered  by  a  rubber  pillow  filled  with 
water,  should  be  so  placed  in  the  bath  that  the  patient  can  lie  upon 
it  without  coming  in  contact  with  the  metal. 

Eulenburg,  in  the  use  of  the  galvanic  current  water-bath,  differ- 
entiates the  kathodal  and  anodal  baths  :  in  the  former  the  water 
constitutes  the  negative,  in  the  latter  the  positive,  pole. 

In  the  dipolar  bath  the  body  of  the  patient  does  not  come 
in  contact  with  either  of  the  electrodes,  but  these  are  immersed  in 
the  water,  one  at  each  end  of  the  tub.  The  number  of  such  elec- 
trodes may  be  increased,  and  in  such  case  they  are  so  placed  in  the 


HYDRO-ELECTRIC    BATHS 


203 


sides  of  the  tub  that  they  are  covered  by  the  water  but  cannot  come 
directly  in  contact  with  the  patient. 

The  source  of  current  supply  may  be  either  a  battery  or 
a  central  station;  if  a  battery,  it  may  be  placed  at  any  dis- 
tance from  the  tub.  The  apparatus  for  current  control  should 
be  placed  in  the  bath-room  itself,  and  should  be  the  same  as  other 


FIG.  145. — SIMPLE  FORM  OF  ELECTRIC  BATH-TUB. 

controllers  used  for  current  application.  Such  an  electric  bath-tub 
of  very  simple  form,  as  made  by  Hirschmann,  is  shown,  with 
its  various  accessories,  in  figure  145. 

Cautery. 

The  heating  effect  of  the  electric  current  may  be  utilized  directly 
for  the  purpose  of  raising  the  temperatures  of  suitably  shaped 
platinum  wires  to  a  red  or  white  heat ;  the  wires  so  heated  are  used 


FIG.  146. — HANDLE  AND  VARIOUS  ELECTRIC  CAUTERY  ENDS. 
204 


ELECTRIC    CAUTERY  2C>5 

for  cauterizing  purposes.  Electric  cautery  ends  of  various  shapes 
are  shown  in  figure  146. 

A  very  strong  current  is  required  for  thus  heating  platinum 
wires  of  the  thickness  needed  for  cautery  operations,  for  most  of 
the  burners  require  from  fifteen  to  twenty  amperes,  and  in  order 
to  keep  a  current  of  this  strength  constant,  even  for  a  few  minutes, 
large  cells  are  necessary.  The  resistance  of  the  external  circuit, 
however,  being  very  low,  a  small  number  of  cells  of  a  low  internal 
resistance  will  suffice  for  the  production  of  such  a  current.  We 
must  not,  however,  forget  that  the  quantity  of  current  necessary 
for  the  heating  of  a  cautery  knife  depends  also  upon  the  radiating 
surface  that  it  possesses,  so  that  a  broad  flat  knife  requires  more 
current  than  a  narrow  one. 

The  majority  of  cells  are  not  suitable  for  cautery  purposes, 
on  account  of  their  high  internal  resistance.  The  Bunsen  and 
Grove  cells  are  too  troublesome  to  be  of  practical  use.  The  best 
cells  for  cautery  purposes  are  undoubtedly  the  bichromate. 
The  chief  objection  to  their  use  is  their  inconstancy,  but  if  they  are 
made  of  ample  size,  they  will  be  sufficiently  constant  for  all  cautery 
operations. 

It  must,  however,  be  clear  that  a  current  sufficiently  powerful  to  be 
used  for  cautery  purposes  can  be  more  easily  obtained  from  a  cen- 
tral station  line  than  from  batteries.  Various  devices  have  accord- 
ingly been  constructed  for  the  purpose  of  utilizing  directly  the  cur- 
rent from  the  main.  Among  the  first  of  these  was  a  rheostat  of 
twenty  amperes  capacity.  Here,  however,  in  order  to  have  the  use 
of  a  comparatively  small  quantity  of  energy,  an  enormous  quantity 
is  wasted,  and  an  intense  heat  is  generated  in  the  rheostat  in  a  very 
short  time.  This  appliance  proved  very  inconvenient,  because  a 
shunt  current  of  an  intensity  of  about  ten  volts  only  had  to  be 
obtained  in  order  to  avoid  the  heating  of  the  contact  and  of  the 
cautery  handle.  The  use  of  a  motor  dynamo  seems  to  offer  a 
better  source  of  current  for  cautery  work.  This  apparatus  may 
be  called  a  rotary  transformer,  and  consists  of  a  machine 
of  one  common  field  and  two  windings  on  one  armature,  each 
winding  having  its  proper  commutator.  The  1 10  volt  current 
used  as  a  motive  power  is  passed  through  a  fine  wire,  and  is 


2O6      APPARATUS  FOR  ALTERING  ELECTROMOTIVE  FORCE 

returned  in  a  transformed  state,  fit  to  heat  cautery  electrodes 
and  snares.  Or  the  no  volt  direct  current  may  be  utilized  for 
cautery  purposes  by  placing  collector  rings  upon  the  armature  shaft, 
and  connecting  them  to  opposite  segments  of  the  commutator; 
from  these  collecting  rings  an  alternating  current  is  obtained  that  is 
nearly  of  the  same  intensity  as  the  current  from  the  main,  but  is 
easily  transformed  by  means  of  a  proper  step-down  transformer. 

It  is,  however,  my  conviction  that  these  outfits  as  to-day  placed 
upon  the  market  are  mere  toys.  For  efficient  work  a  motor  of  less 
than  one-quarter  horse-power  is  entirely  out  of  the  question.  I 
believe  that  a  good  storage  battery  is  more  reliable  and  more 
economical  for  cautery  work  than  any  of  the  preceding  appliances. 

Storage  cells,  called  also  accumulators  or  secondary  cells,  are 
made  in  a  number  of  forms.  The  principle  of  their  formation  is  the 
following :  If  two  lead  plates  or  lead  grids  containing  lead  oxid  are 
immersed  in  dilute  sulphuric  acid,  and  through  such  a  cell  a  con- 
stant current  is  passed,  oxygen  will,  through  electrolytic  decompo- 
sition of  the  water,  collect  at  the  plate  through  which  the  current 
enters,  and  will  combine  with  PbO  to  form  PbO2 ;  upon  the  other 
plate  hydrogen  collects  and  reduces  the  lead  oxid  to  metallic  lead, 
which,  in  a  finely  divided  form,  constitutes  the  so-called  porous  lead, 
or  lead  sponge.  When  all  the  lead  oxid  has  thus  been  trans- 
formed, the  storage  cell  is  charged  to  its  full  capacity.  If,  now,  this 
cell  be  disconnected  from  the  charging  source  and  the  free  ends  of 
the  two  lead  plates  be  connected  by  a  conductor,  a  current  will  flow 
through  this  conductor  in  a  direction  opposed  to  that  of  the  charg- 
ing current.  This  current  flow  will  continue  until  both  lead  plates 
have  returned  to  their  original  conditions.  The  cell  is  then  dis- 
charged, and  must  be  recharged  for  further  use. 

Storage  cells  are  now  manufactured  so  that  they  may  easily  be 
transported,  and  will  give  perfect  satisfaction  if  used  constantly. 
When  a  battery  is  to  be  used  for  occasional  work,  a  storage  battery 
should  not  be  selected.  Storage  batteries  are  best  charged  from 
a  direct  line.  In  order  to  prevent  too  great  a  flow  of  current, 
resistance  must  be  inserted  into  the  circuit  in  the  shape  either  of 
incandescent  lamps  or  iron  wire  coils.  The  positive  wire  of  the  line 
must  be  connected  with  the  positive  pole  of  the  battery,  the  negative 


EXPLORING    LAMPS 


2O7 


wire  of  the  line,  with  the  negative  pole  of  the  battery.  Full  direc- 
tions as  to  time  of  charging,  care  of  cells,  etc.,  accompany  all  pur- 
chasable batteries. 

Exploring   Lamps. 

A  thin  platinum  wire  or  a  fine  carbon  filament  connected  in  the 
circuits  of  several  cells  of  high  electromotive  force  and  low  internal 
resistance  will  be  heated  to  an  incandescent  state.  Such  uncovered 
incandescent  platinum  spirals  have  been  made  use  of  in  connection 
with  small  metallic  reflectors,  for  the  purpose  of  direct  illumination 


FIG.  147. — SET  OF  MINIATURE  EXPLORING  LAMPS. 

and  visual  examinations  of  the  accessible  body-cavities.  On  account, 
however,  of  the  heat  produced  and  of  the  danger  of  burning  the  tis- 
sues, they  presented  fewer  advantages  than  reflected  daylight  or 
lamplight.  Since  the  discovery  of  the  Edison  filament  of  carbonized 
vegetable  fiber  small  incandescent  lamps  entirely  inclosed  in  an  air- 
tight glass  chamber  have  been  constructed,  whose  introduction  into 
the  body-cavities  is  not  only  feasible,  but  entirely  unobjectionable. 
A  set  of  such  miniature  lamps  is  shown  in  figure  147.  Such  ex- 
ploring lamps  require  a  current  pressure  of  from  four  to  fifteen  volts, 
and  a  current  strength  of  from  ^  to  I  ^  ampere. 


208 


APPARATUS  FOR  ALTERING  ELECTROMOTIVE  FORCE 


Care  must  be  exercised  in  the  employment  of  such  lamps  that 
the  pressure  shall  not  exceed  that  for  which  they  are  designed. 
They  may  be  operated  by  a  battery  or  by  a  current  from  the  main 
line.  Under  all  circumstances  a  controller  should  be  used.  If  the 
main  current  of  110  volts  be  employed,  a  50  candle-power  lamp, 
allowing  i^  ampere  of  current  to  pass,  and  a  volt  controller  in 
series  with  the  exploring  lamp,  should  form  the  circuit.  The  con- 
troller having  a  capacity  of  \y2  ampere  need  not  have  a  resistance 


FIG.  148. — LAMP  FOR  USING  REFLECTED 
LIGHT. 


FIG.  149. — THE  WAPPI.ER  ELECTRIC 
CONTROLLER. 


of  more  than  20  ohms.  For  the  use  of  reflected  light  the  ordinary 
filament  is  inadmissible,  as  the  reflection  of  the  filament  in  the  mir- 
ror interferes  with  the  examination.  E.  B.  Meyrovvitz,  of  New 
York,  furnishes  a  lamp  in  which  this  objection  is  overcome  through 
a  spiral  arrangement  of  the  filament.  (See  Fig.  148.)  • 

An  excellent  controller,  made  in  accordance  with  the  principles 
already  enumerated  for  the  regulation  of  the  line  current,  and  adapt- 


ELECTRIC    LIGHT    CONTROLLER  2OQ 

ing  it  for  the  operations  of  small  lamps,  faradaic  coils,  small  motors, 
etc.,  is  made  by  the  Wappler  Electric  Controller  Company,  of  New 
York,  and  is  shown  in  figure  149.  This  apparatus  is  devised  to 
carry  the  current  fora  no  volt  1 6  candle-power  incandescent  lamp. 
In  the  derived  current  from  the  two  binding  posts  a  current  of  80 
volts  and  I  y2  ampere  can  be  obtained,  and  while  the  voltage  can  be 
reduced  by  steps  of  ^  of  a  volt  to  zero,  the  amperage  will  remain 
the  same.  As  a  light-regulating  device,  not  only  for  exploring 
lamps,  but  also  for  use  in  hospital  wards,  sick-rooms,  or  wherever  it 
becomes  necessary  to  lower  a  light  without  completely  extinguish- 
ing it,  its  action  is  unsurpassed. 


CHAPTER  V 
RONTGEN  RAYS  OR  X-RAYS 

Production  of  X-rays.  Characteristics.  Properties.  Source.  Geissler 
Tube.  Crookes  Tube.  Kathode  Rays.  Antikathode.  Focus  Tubes. 
Adjustable  Vacuum  Tubes.  Excitation  by  Influence  Machine.  Excita- 
tion by  Ruhmkorff  Coil.  Condenser.  Interrupter.  Fluoroscope.  Ski- 
agraphy.  Radiographic  Table.  Localization  Methods.  X-Ray  Burns. 

Apparatus  for  the  Production  of  Skiagrams  and  for  the 
Transillumination  of  the  Body  by  Means  of  the  Rontgen 
Rays. 

The  importance  that  the  Rontgen  rays  have  attained  in  sur- 
gical and  medical  diagnosis  for  purposes  of  skiagraph y  and  for 
transillumination  of  the  deep  tissues  and  organs  since  Decem- 
ber, 1895,  when  Professor  Rontgen,  of  Wiirzburg,  announced  his 
discovery,  is  so  great  and  their  promise  of  greater  usefulness  is  so 
far-reaching  that  a  description  of  the  basic  principles  and  necessary 
apparatus  seems  to  be  indispensable  in  a  treatise  like  the  present. 

Without  entering  upon  the  diagnostic  certainties  and  the  thera- 
peutic possibilities  that  this  newly  discovered  form  of  radiation 
offers,  let  us  first  consider  what  these  Rontgen  rays  are. 

Rontgen  discovered  that  glass  tubes  in  which  a  very  high 
vacuum  existed  were  capable,  under  electric  excitation,  of  emit- 
ting a  radiation  for  which  he  proposed  the  name  of  X-rays,  or 
"the  unknown  rays."  No  better  description  of  the  peculiarities 
that  the  Rontgen  rays  possess  can  be  given,  than  that  of  Rontgen 
himself.  He  says  : 

"  When  a  discharge  from  a  large  induction  coil  is  passed  through 
a  Hittorf  vacuum  tube  or  through  a  well-exhausted  Crookes  or 
Lenard  tube,  it  is  possible  to  see,  in  a  completely  darkened  room, 
that  paper  covered  with  barium  platinocyanid  lights  up  with 
brilliant  fluorescence  when  held  toward  the  tube.  Calcium  sul- 


CHARACTERISTICS    OF    X-RAYS  211 

phid,  uranium  glass,  Iceland  spar,  rock-salt,  and  other  bodies  also 
fluoresce,  and  the  origin  of  this  fluorescence  is  within  the  tube,  as 
can  easily  be  demonstrated. 

'  This  influence  penetrates  objects  opaque  to  ultra-violet  light, 
sunlight,  or  arc  light.  Water  and  other  like  fluids,  organic  sub- 
stances, such  as  paper,  wood,  and  tissues  of  the  body,  are  ex- 
tremely transparent  to  it,  while  metals,  inorganic  salts,  etc.,  are 
much  less  so ;  but  no  body  is  completely  opaque.  It  is  chiefly  their 
density  that  affects  the  permeability  of  bodies.  The  rays  have  no 
calorific  effect  and  are  invisible  to  the  eye.  They  are  not  deflected 
by  prisms,  nor  reflected,  refracted,  or  contracted  by  lenses.  Bodies 
behave  toward  the  rays  as  turbid  media  to  light.  The  intensity 
of  the  fluorescent  light  varies  nearly  as  the  inverse  square  of  the 
distance  between  the  screen  and  the  discharge  tube.  The  air  ab- 
sorbs these  rays  much  less  than  it  does  the  kathode  rays.  The 
X-rays  are  not  deviated  by  a  magnet.  The  place  of  most  brilliant 
phosphorescence  of  the  wall  of  the  discharge  tube  is  the  chief  seat 
whence  the  rays  originate  and  spread  in  all  directions — i.  e.,  they 
proceed  from  the  front,  where  the  kathode*  rays  strike  the  glass, 
and  if  the  latter  are  deviated  by  a  magnet,  the  X-rays  proceed  from 
the  new  point  at  which  the  kathode  rays  end. 

'  Of  special  interest  is  the  fact  that  photographic  dry  plates  are 
sensitive  to  these  new  rays.  It  is  thus  possible  to  exhibit  this 
phenomenon  so  as  to  exclude  the  danger  of  error.  I  have  thus 
confirmed  many'  observations  originally  made  with  observations 
with  the  eye  through  the  fluorescent  screen.  Here  the  power 
of  rays  to  pass  through  wood  or  cardboard  becomes  useful.  The 
photographic  plate  can  be  exposed  to  their  action  without  removing 
the  protecting  case,  so  that  experiments  need  not  be  conducted  in 
darkness.  A  regular  shadow  picture  is  produced  by  the  interposi- 
tion of  a  more  or  less  permeable  body  between  the  source  of  rays 
and  the  photographic  plate  or  fluorescing  screen." 

The  salient  peculiarities  therefore  are  : 

That  these  rays  produce  no  excitation  of  the  optic  nerve  and  are 
therefore  invisible  to  the  naked  eye. 

That  they  possess  the  power  of  traversing  substances  opaque  to 
ordinary  light. 


212  RONTGEN    RAYS    OR    X-RAYS 

That  they  possess  the  power  of  producing  fluorescence  in  certain 
bodies  upon  which  they  strike. 

That  they  are  capable  of  affecting  sensitized  photographic  plates. 

The  rays  may  be  produced  by  the  discharge  from  any  source  of 
sufficiently  high  tension,  through  a  proper  tube. 

The  Tube. 

The  Geissler  tube,  so  well  known  to  every  student  of  physics, 
is  a  low  vacuum  tube,  hermetically  sealed,  usually  exhausted 
to  about  y^Vo"  °f  an  atmosphere,  into  which  project  metallic  termi- 
nals that  may  be  connected  with  the  poles  of  a  source  of  electricity 
of  high  potential.  In  1879  William  Crookes,  of  London, 
devised  a  new  form  of  tube  having  a  high  vacuum,  the  tube 


FIG.  150. — SHOWING  THE  COURSE  TAKEN  BY  AN  ELECTRIC  DISCHARGE  IN  A 

CROOKES  TUBE. 

being  exhausted  to  about  Ioo^ooo  of  an  atmosphere.  If  the  ter- 
minals of  a  Geissler  or  low  vacuum  tube  be  connected  with  an 
influence  machine,  the  poles  of  the  machine  and  the  poles  of  the 
tube  corresponding,  a  band  of  light  will  be  produced  and  the  dis- 
charge will  take  place  between  the  kathode  and  the  anode ;  if, 
on  the  other  hand,  a  Crookes  tube  be  similarly  connected,  a  fluores- 
cence will  set  in,  and  the  discharge  from  the  kathode  will  pass 
in  straight  lines  to  the  opposite  wall  of  the  tube,  regardless  of  the 
anode,  which  is  usually  placed  at  any  indifferent  point  on  the  side. 
(See  Fig.  150.) 

These  kathode  rays  are  generally  believed  to  consist  of 
streams  of  negatively  electrified  particles.  This  belief  is  supported 
by  the  fact  that  the  rays  are  capable  of  deflection  by  a  magnet. 


X-RAY    TUBES  213 

At  whatever  point  these  kathode  rays  impinge,  fluorescence  and 
heat  are  produced,  and  it  is  this  fluorescent  part  that  is  the  seat,  or 
origin,  of  the  Rontgen  rays. 

In  order  to  obtain  as  great  a  concentration  of  kathode  rays 
as  possible,  and  therefore  a  corresponding  concentration  of  X-rays, 
a  special  arrangement  of  the  tube  must  be  made.  The  kathode 
rays  could  easily  be  focused  upon  a  single  point  of  the  tube  by 
making  the  kathode  concave.  But  if  the  kathode  were  concave 
and  the  rays  thus  focused  upon  a  single  small  part  of  the  tube, 
the  heat  produced  at  this  point  would  be  so  great  as  to  fuse  the 
glass.  This  is  overcome  by  introducing,  at  the  point  upon  which 
the  focused  kathode  rays  impinge,  a  piece  of  platinum  foil  (Fig.  151) 
placed  at  an  angle.  These  rays  are  thus  concentrated  upon  a  small 
surface,  the  heating  of  \vhich,  it  being  platinum  and  not  being 


FIG.  151. — AN  X-RAY  TUBE. 

in  contact  with  the  glass  of  the  tube,  in  no  way  damages  the 
latter.  This  piece  of  foil  is  called  the  antikathode,  and  becomes 
the  source  of  the  X-rays. 

In  all  such  focusing  tubes  the  kathode  rays  are  partially  reflected 
from  the  antikathode  and  impinge  upon  the  walls  of  the  tube,  and 
there  also  excite  X-rays,  which,  however,  do  not  interfere  with  the 
rays  produced  at  the  antikathode  itself.  Such  tubes  are  con- 
structed of  various  shapes. 

The  focus  tube  with  adjustable  vacuum  is  the  latest 
development  of  this  kind  of  tube.  Such  a  tube  is  made  by  the 
Edison  Manufacturing  Company,  and  is  shown  in  figure  152.  It 
possesses  the  advantage  over  the  ordinary  focus  tube  of  admitting 
of  a  lowering  of  the  vacuum  in  the  tube  by  shortening  or  length- 


214 


RONTGEN    RAYS    OR    X-RAYS 


ening  the  space  between  the  spark  rods  of  the  adjuster.  Messrs. 
Queen  &  Co.  make  a  tube  (Fig.  153)  in  which  the  vacuum  is 
adjustable  and  is  kept  constant  at  the  desired  point  by  means  of 
an  automatic  device. 

A  reference  to  the  illustration  will  make  the  operation  of  the 
tube  clear.  A  small  bulb  containing  a  chemical  that  gives  off 
vapor  when  heated,  and  reabsorbs  it  when  it  cools,  is  directly  con- 
nected with  the  main  tube,  and  is  surrounded  by  an  auxiliary  tube 
exhausted  to  a  low  Crookes  vacuum,  the  kathode  being  so  placed 
as  to  heat  the  bulb  by  the  bombardment  of  the  kathode  rays.  This 


FIG.  152. — Focus  TUBE  WITH  ADJUSTABLE  VACUUM. 

kathode  is  connected  to  an  adjustable  spark  point,  the  end  of  which 
may  be  swung  to  any  desired  distance  from  the  kathode  of  the 
main  tube.  The  anode  of  the  small  tube  is  directly  connected  with 
the  anode  of  the  main  tube.  The  coil  is  connected,  as  usual,  with 
the  main  tube,  which  has  been  exhausted  to  a  very  high  vacuum 
and  consequently  has  a  high  resistance ;  the  current,  therefore, 
takes  the  path  of  least  resist  a  nee  by  the  spark  point  and 
the  auxiliary  tube,  and  heats  the  chemical  in  the  small  bulb, 
thereby  releasing  the  vapor  that  it  contains  in  state  of  absorption 
and  driving  it  into  the  main  tube.  This  will  continue  for  a  few 


ADJUSTABLE    VACUUM    TUBES 


215 


seconds  until  sufficient  vapor  has  been  driven  into  the  main  tube  to 
bring  down  its  resistance  to  that  of  the  spark  gap  plus  the  small 
resistance  of  the  auxiliary  bulb,  when  the  current  will  pass  through 
the  main  tube.  After  this  only  an  occasional  spark  will  jump 
across  the  gap  to  counteract  the  tendency  of  the  chemical  to  re- 
absorb  vapor  as  its  bulb  cools,  thus  raising  the  resistance  of  the 
main  tube.  The  tube  is  thus  maintained  at  a  constant  vacuum 
while  running.  When  the  current  is  stopped,  the  chemical  cools 


FIG.  153. — QUEEN  SELF-REGULATING 
X  RAY  TUBE. 


FIG.  154. — AUTOMATIC  ADJUSTABLE 
VACUUM  X-RAY  TUBE,  FOR  USE  WITH 
ALTERNATING  CURRENTS. 


off  and  reabsorbs  vapor,  and  the  tube  returns  to  its  starting  condi- 
tion of  high  vacuum. 

The  tube  may  be  set  to  run  at  high  vacuum  by  placing  the  spark 
point  at  a  considerable  distance  from  the  kathode  terminal  of  the 
main  tube,  or  to  run  low  by  placing  it  near  the  latter.  A  special 
form  of  tube  on  the  same  principle  has  been  constructed  for  use 
with  alternating  currents  (Fig.  1 54). 

The  adjustability  of  the  vacuum  is  of  the  utmost  importance,  as 


2l6 


RONTGEN    RAYS    OR    X-RAYS 


the  penetrating  power,  photographic  effect,  and  ability  brilliantly  to 
light  a  fluorescing  screen  all  depend  on  the  degree  of  exhaustion  ; 
and  that  degree  of  vacuum  which  is  best  for  one  operation  is  not 
so  for  another. 

Exciting  Current. 

The  next  most  important  factor  in  the  production  of  these  rays  is 
the  apparatus  necessary  for  the  production  of  the  exciting  current. 
Currents  from  a  high  tension  source  are  requisite.  Such  currents 
may  be  obtained  from  a  powerful  static  machine  or  from  a 
Ruhmkorff  coil  operated  by  the  currents  of  a  primary  bat- 
tery, secondary  battery,  or  central  station. 


FIG.  155. — SHOWING  THE  ATTACHMENT  OF  X-RAY  TUBE  TO  STATIC  MACHINE. 

If  the  static  machine  be  used,  the  tubes  should  be  connected 
directly  to  the  prime  conductors  without  the  intervention  of  Ley- 
den  jars,  as  is  shown  in  figure  155,  but  in  my  experience  it  -has 
proved  better  that  a  spark  gap,  if  possible  an  adjustable  one, 
should  be  left  between  one  pole  of  the  machine  and  the  correspond- 
ing pole  of  the  tube.  By  means  of  this  spark  gap  the  discharge 
through  the  tube  becomes  oscillatory. 

For  the  excitation  of  small  tubes  an  influence  machine  gives 
fairly  good  results  ;  but  when  powerful  tubes  are  to  be  excited,  it  is 
necessary  not  only  to  employ  machines  with  large  plates,  giving  a 
spark  of  sufficient  length,  but  the  quantity  of  electricity  also  must 
be  increased  by  a  suitable  increase  in  the  number  of  plates.  The 


EXCITING    AND    INTERRUPTING    APPARATUS  2 1/ 

amperage  of  even  the  largest  influence  machines  is,  however, 
insufficient  to  enable  us  to  obtain  as  satisfactory  results  as  with  a 
suitable  Ruhmkorff  coil,  excited  through  a  vibrator  or  revolving 
circuit  breaker. 

The  Ruhmkorff  coil  to  be  used  should  be  specially  constructed 
for  the  purpose  in  view,  for  in  the  use  of  the  high  voltage  that  is 
necessary,  the  insulation  between  the  primary  and  the  secondary 
coil  must  be  so  perfect  that  under  no  circumstances  can  a  spark 
discharge  take  place  from  the  primary  to  the  secondary  coil.  Such 
an  occurrence  is  always  due  to  the  defective  construction  of  the 
apparatus.  The  Ruhmkorff  coil  once  set  up,  requires  no  special 
attention,  particularly  if  the  interrupter  is,  as  it  should  be,  separated 
from  the  coil  and  joined  to  the  remainder  of  the  necessary  appa- 
ratus. The  condenser  may  form  one  piece  with  the  coil  or  may  be 
separated  from  it.  The  induction  coil  may  be  operated  by  a  p  ri- 
maryor  storage  battery,  by  continuous  electric-light 
circuit,  or  by  alternating  current  electric-light  circuit.  In 
each  instance  the  coil  should  be  specially  adapted  to  the  source  of 
the  current.  In  all  cases  a  switch  for  reversing  the  current 
is  necessary,  so  that  the  kathode  can  be  brought  opposite  the 
reflector  in  the  tube. 

Induction  coils  for  use  with  X-ray  tubes  are  usually  estimated  as  to 
their  strength  by  the  secondary  sparking  distance,  the  greater 
sparking  distance  corresponding  to  a  greater  electric  force,  thus 
enabling  a  more  powerful  tube  to  be  operated. 

In  addition  the  apparatus  consists  of:  (i)  An  interrupter;  (2) 
a  rheostat  for  current  regulation  ;  (3)  the  accessory  apparatus 
for  transillumination  and  for  facilitating  skiagraphic  im- 
pressions. 

The  Interrupter. — Various  kinds  of  interrupters  may  be  em- 
ployed. A  spring  platinum  interrupter  is  serviceable  only  with 
a  coil  giving  a  spark  of  not  more  than  25  centimeters,  and  then  only 
with  a  battery  current.  The  destruction  of  the  platinum,  in  conse- 
quence of  the  unavoidable  large  spark  passing  between  it  and  the 
adjusting  screw,  is  so  great  and  so  rapid  that  very  soon  there  is  in- 
sufficient contact  and  consequent  irregularity  of  action.  A  better 
interrupter  consists  of  a  metallic  wheel  attached  to  an  electro- 


2l8  RONTGEN    RAYS    OR    X-RAYS 

motor  ;  this  wheel  is  provided  with  gaps  on  its  periphery  upon 
which  brushes  rest,  so  that  the  circuit  is  interrupted  a  number  of 
times  during  each  revolution  of  the  wheel. 

When,  however,  a  no  volt  continuous  current  is  employed  to 
excite  the  coil,  some  arrangement  should  be  provided  by  means  of 
which  the  sparks  may  promptly  be  extinguished,  and  thus  the  cir- 
cuit be  broken  quickly.  Figure  154  shows  such  an  apparatus, 
known  as  the  Edison  instantaneous  air-breaking  wheel. 

The  device  consists  of  two  tooth  wheels  mounted  upon  the  same 
shaft.  The  projections,  or  teeth,  make  contact  with  two  flat 
brushes  that  bear  on  the  outer  peripheries,  and  by  which  the  cur- 
rent is  brought  in  and  let  out  again.  These  wheels  are  rotated  at 
a  very  high  speed  by  a  small  direct  current  motor  that  also  runs  a 


FIG.  156. — EDISON  INSTANTANEOUS  AIR-BREAK  WHEEL. 

pressure  blower.  The  air  blast  from  the  blower  enters  a  bifurcated 
tube,  and  is  conducted  to  two  flat  nozles  immediately  over  the  con- 
tact brushes. 

When  the  device  is  set  in  operation  by  starting  the  motor  and 
connecting  the  primary  pole  of  the  induction  coil  in  series  with 
the  binding  posts  provided  for  this  purpose,  the  spark  formed  at 
the  contact  brushes,  when  the  coil  is  energized,  is  blown  out  in- 
stantaneously by  the  air  blast  at  the  moment  of  formation.  This 
greatly  increases  the  rapidity  of  change  in  the  magnetic  circuit,  and 
vastly  augments  the  electromotive  force  in  the  secondary  coil. 

The  rheostat  to  be  used  requires  no  special  description  ;  it  must, 
of  course,  be  adapted  to  the  current  employed. 

The  Fluoroscope. — If,  in  a  darkened  room,  an  excited  tube  be 


FLUOROSCOPY  219 

placed  in  a  cardboard  box  into  which  no  ordinary  light  can  enter, 
no  light  from  the  excited  tube  will  be  seen  on  the  outside  of  the 
box.  If,  however,  one  side  of  a  screen  of  wood  or  cardboard  be 
covered  with  some  suitable  fluorescent  material,  as  barium 
platinocyanid  or  calcium  tungstate,  and  this  screen  be 
held  with  its  coated  side  to  the  eye  of  the  observer,  the  screen 
will  be  seen  to  fluoresce,  from  the  excitation  of  the  X-rays  that 
have  passed  through  the  box  and  the  wood  or  cardboard  of  the 
screen.  A  metallic  object  held  against  the  board  of  the  screen, 
between  this  and  the  source  of  the  X-rays,  will  intercept  these  rays 
and  cast  a  shadow  upon  the  active  surface  of  the  screen,  so  that  the 
eye  will  see  a  dark  shadow  of  the  metallic  object  surrounded  by  a 


FIG.  157. — FLUOROSCOPE. 

fluorescent  field.  Upon  this  principle  the  fluoroscope  is  constructed. 
It  consists  of  a  light-tight  box  (Fig.  157),  very  similar  in  shape  to  a 
stereoscope,  the  small  end  having  an  aperture  and  made  to  fit 
tightly  over  the  eyes  and  bridge  of  the  nose ;  the  inner  surface  of 
the  broad  end  is  covered  with  a  uniform  layer  of  fine  crystals  of  fluo- 
rescent material.  This  latter  constitutes  the  fluorescent  screen, 
and  is  the  essential  feature.  If,  now,  the  examiner  place  his  eyes 
to  the  narrow  end,  and  the  extended  hand  be  held  against  the  broad 
end  of  the  fluoroscope  so  that  it  comes  between  this  and  the  source 
of  the  rays,  the  shadows  of  the  bones  of  the  hand,  and  less-marked 
shadows  of  the  tissues,  will  be  seen  upon  the  screen  instead  of  the 
general  fluorescence. 


22O  RONTGEN    RAYS    OR    X-RAYS 

The  fluoroscope  may  similarly  be  applied  to  the  examination  of 
any  portion  of  the  body  penetrable  by  the  X-ray  without  prolonged 
exposure.  By  its  use  not  only  so-called  surgical  lesions,  as  of  bones 
and  joints,  and  the  presence  of  bullets  and  other  foreign  bodies  may 
be  detected,  but  the  thoracic  viscera  may  be  examined,  and,  with 
less  satisfaction,  the  abdominal  contents.  It  is  of  signal  use  in  de- 
termining the  size  and  position  of  the  heart,  the  presence  or  absence 
of  aneurysms  (see  Fig.  1 59)  and  other  tumors  of  the  mediastinum, 
the  presence  or  absence  of  pleural  adhesions  and  effusions,  etc.,  and 
may  in  some  cases  render  possible  the  veiy  early  diagnosis  of  pul- 
monary tuberculosis.  In  more  advanced  cases  its  revelations  may 
confirm  or  correct  the  inferences  drawn  from  percussion  and  aus- 
cultation. 

Skiagraphy. — The  taking  of  a  skiagraphic  reproduction  on  a 
sensitized  plate  by  means  of  X-rays  offers  no  difficulty.  Accord- 
ing to  the  necessity,  the  tube  is  so  fastened  in  the  standard  that 
the  rays  take  a  horizontal  or  a  vertical  direction.  Plates  equally 
sensitive  to  ordinary  daylight  seem  to  be  variously  sensitive  to  the 
X-rays,  and  silver  bromid  gelatin  emulsion  plates  seem  to  be  best 
adapted  to  give  the  most  satisfactory  results.  No  camera  is 
employed.  The  sensitized  plate  is  secured  in  an  ordinary  plate- 
holder,  or  is  completely  enveloped  in  black  paper.  The  object  of 
which  we  wish  to  get  a  skiagraphic  print  is  placed  between  the  sen- 
sitized plate  and  the  source  of  the  rays,  always  being  sure  that 
the  sensitized  surface  of  the  plate  is  nearest  to  the  object  to  be  re- 
produced. 

The  tube  is  set  up  at  the  distance  best  suited  to  its  power,  and 
this  varies  from  one  to  three  feet.  The  time  of  exposure  will  vary 
also  according  to  the  energy  of  the  tube,  and  will  depend  upon  the 
kind  of  plate  employed  and  upon  the  thickness  of  the  tissues  to  be 
penetrated  by  the  rays.  With  a  good  apparatus,  from  fifteen  to 
thirty  seconds'  exposure  should  suffice  for  the  hand,  from  three  to 
eight  minutes  for  the  hip-joint,  and  eight  to  ten  minutes  for  the 
thorax  or  abdomen.  The  plate  is  then  developed  by  the  usual 
methods  of  photography. 

A  reproduction  of  a  skiagram  of  the  hand  is  shown  in  figure 
158.  This  picture  is  taken  from  the  right  hand,  with  the  palmar 


SKIAGRAM 


221 


FIG.  158. — A  SKIAGRAM. 


222  RONTGEN    RAYS    OR    X-RAYS 

surface  toward  the  sensitized  plate.  At  first  glance  it  seems  to 
be  the  left  hand  and  not  the  right,  but  this  is  an  error  that  must 
be  guarded  against.  It  is  easily  seen  that  in  the  developed  plate 
the  lights  appear  dark  and  the  shadows  appear  light ;  so  from  the 
point  of  view  of  lights  and  shadows  the  plate  is  a  negative,  but  in 

Left.  Right. 


FIG.  159. — SKIAGRAM  OF  ANEURYSM  OF  THE  TRANSVERSE  ARCH  OF  THE  AORTA. — 
(Plate  by  Professor  Arthur  Goodspeed,  from  a  case  oj  Dr.  S.  Solis-Coherf s.) 

Above  the  shadow  of  the  pericardial  sac  and  its  contents  is  seen  the  shadow  of  the 
aneurysm,  involving  especially  the  transverse  portion  of  the  aortic  arch.  Through 
the  normal  lungs  the  radiations  pass  unobstructed.  The  plate  being  placed  over 
the  sternum  and  the  tube  at  the  back  of  the  patient,  the  relations  of  right  and  left 
in  the  picture  are  as  if  seen  from  behind. 

all  other  respects  the  plate  is  a  positive.  The  contours  are  abso- 
lutely reproduced  in  silhouette  form.  Therefore  the  print  from  this 
plate,  although  its  lights  and  shadows  are  correctly  reproduced,  is 
a  negative,  or  the  reverse  of  the  original  outline  figure. 

Figure   159  shows  an  aneurysm  of  the  transverse  arch  of  the 


LOCALIZATION    APPARATUS  223 

aorta.1      Pelvic  tumors,  renal  calculi,  and  other  abdominal  lesions 
have  been  demonstrated  in  a  similar  way. 

Radiographic  Table  and  Localization  Apparatus. 

Various  appliances  ordinarily  at  hand  can  be  utilized  for  holding 
the  tubes  and  for  placing  the  patient  in  position  for  skiagraphic  and 
fluoroscopic  examinations  ;  but  adjustable  standards  and  tables  spe- 
cially designed  for  the  purpose  are  supplied  by  manufacturers  and 
greatly  facilitate  the  work.  Especially  are  these  appliances  desir- 
able when  it  is  necessary  accurately  to  locate  foreign  bodies,  calculi, 
tumors,  etc.  Messrs.  Queen  &  Co.,  of  Philadelphia,  have  built  for 
the  Polyclinic  Hospital  of  that  city,  after  suggestions  of  Dr.  C.  L. 
Leonard,  a  radiographic  table,  the  use  of  which  is  shown  in  figures 
1 60  and  161.  It  is  made  in  two  sections,  each  three  feet  in  length, 
together  with  a  small  foot-board.  Both  the  foot-board  and  one 
length  of  the  table  are  adjustable  at  various  angles  to  the  horizon, 
in  order  to  admit  of  adaptation  to  different  cases.  The  top  of  the 
table  is  of  thin  fiber  sheet,  which  is  very  tough,  and  at  the  same 
time  transparent  to  the  X-rays.  The  plate-holders  consist  of  re- 
movable backs,  four  in  number,  eighteen  inches  long  and  fifteen 
inches  wide,  having  a  perfectly  flat  top  surface.  The  tube  can  be 
placed  in  any  position  above  or  below  the  table,  and  if  the  plate- 
holders  be  removed,  it  offers  an  excellent  method  of  fluoroscopic 
examination. 

In  localizing  a  foreign  body,  calculus,  or  other  object  in  the  body, 
it  is  a  simple  matter  to  take  one  picture,  shift  the  position  of  the 
tube,  change  plates,  and  take  another  picture,  without  in  any  way 
disturbing  the  patient.  The  localization  apparatus  shown  in  figure 
162  is  employed,  and  from  the  different  positions  of  the  shadows 
of  the  ball  of  the  indicator  and  of  the  foreign  body  on  the  two 
plates,  the  location  of  the  latter  is  calculated.  For  the  localiza- 
tion of  foreign  bodies  in  the  eye,  Dr.  W.  M.  Sweet,  of  Phila- 

1  The  case,  occurring  in  the  practice  of  the  editor,  was  of  great  interest,  as  with  the 
exception  of  localized  dullness  at  the  upper  portion  of  the  sternum,  the  usual  physical 
signs  of  the  condition  were  absent.  The  peculiar  character  of  the  cough  suggested 
fluoroscopic  search  for  aneurysm,  and  a  permanent  record  of  the  findings  was  made  in 
the  skiagram. 


224 


RONTGEN    RAYS    OR    X-RAYS 


delphia,  has  devised  a  special  method,  the  application  of  which  is 
shown  in  figure  163.  Two  radiographs  are  made,  to  give  different 
relations  of  the  shadows  of  the  indicators  and  of  the  foreign  body : 


one  with  the  tube  horizontal,  or  nearly  so,  with  the  plane  of  the 
indicators,  and  rtie  second  with  the  tube  at  any  distance  below  this 
plane.  Two  circles  are  drawn,  one  to  represent  a  horizontal,  and 


SKIAGRAPHY 


225 


15 


226 


RONTGEN    RAYS    OR    X-RAYS 


the  other  a  vertical,  section  of  the  normal  eyeball,  and  upon  these 
circles  are  noted  the  relative  position  of  the  indicators  when  the 
exposures  are  made.  If  measurements  of  the  positions  of  the 
shadows  of  the  indicators,  as  shown  upon  the  plates,  are  entered 
upon  these  circles,  and  lines  drawn  through  the  points  of  measure- 
ment, the  position  of  the  foreign  body  in  the  eye  must  be  at  the 
crossing  of  these  lines,  representing  the  planes  of  shadow  of  the  two 
exposures. 


FIG.  162. — LOCALIZATION  APPARATUS. 


X-ray  Dermatitis. — This  is  the  most  convenient  place  to  intro- 
duce a  necessary  word  of  caution.  Irritation  of  the  skin,  inflamma- 
tion, and  even  extensive  and  severe  burns  may  result  from  too  pro- 
longed exposure  to  the  X-rays.  These  accidents  were  more  common 
in  the  early  days  of  skiagraphy.  They  are  to  be  avoided  by  care 
as  to  the  duration  of  the  sitting  and  as  to  the  distance  of  the  tube 
from  the  body  of  the  patient.  The  longer  the  necessary  duration 
of  the  exposure,  the  greater  should  be  the  distance  between  the 
tube  and  the  body.  Some  observers  state  that  severe  burns  occur 
only  when  tubes  of  low  vacuum  are  used.  Others  interpose  an 


OPHTHALMIC    LOCALIZATION 


227 


aluminum  screen  between  the  tube  and  the  patient  and  claim  thus 
to  avoid  the  liability  to  produce  burns. 

Some  persons  manifest  a  peculiar  susceptibility  to  the  caustic 
action  exerted  by,  or  accompanying,  the  Rontgen  rays,  and  this 
cannot  be  predetermined ;  so,  also,  the  very  young,  the  aged,  and 
the  debilitated  are  less  resistant  than  others.  In  the  absence  of 
special  idiosyncracy  in  persons  of  average  strength  thirty  min- 
utes may  be  considered  the  maximum  duration  of  exposure,  and 


FIG.  163. — DR.  SWEET'S  APPLIANCE  FOR  LOCALIZING  FOREIGN  BODIES  IN  THE  EYE. 

ten  inches  the  least  distance  of  the  tube  from  the  body,  permissible. 
A  number  of  exposures  at  brief  intervals  should  be  counted  as  one 
in  estimating  time.  As  the  burn  is  not  usually  evident  until  two 
or  three  days  after  exposure,  prolonged  sittings  should  not  ordi- 
narily be  repeated  without  an  interval  of  at  least  forty-eight  hours. 
No  satisfactory  explanation  of  the  irritant  influence  of  the  radia- 
tion has  been  given,  but  attempts  have  been  made  to  utilize  it, 
under  proper  control,  in  therapeutics. 


INDEX  OF  PROPER  NAMES 


Ampere,  Andr6  Marie,  73 
d'Arsonval,  A.,  200 

Brenner,  Rudolf,  138 
Bunsen,  Robert  Wilhelm,  51 

Cohen,  S.  Solis,  223 
Crookes,  William,  212 

Daniell,  John  Frederick,  48 
Dubois-Reymond,  Emil,  194 

Edelmann,  M.  Th.,  156,  196 
Edison,  Thomas  Alva,  214,  218 
Engelmann,  George,  193 
Eulenberg,  Albert,  202 

Faraday,  Michael,  72,  95,  98,  100 
Flemming,  Otto,  159,  193 
Franklin,  Benjamin,  23,  43,  134 

Gaiffe,  A.,  141,  156 
Galvani,  Luigi  Aloisio,  47 
Geissler,  Heinrich,  212 
Glaeser,  Hermann,  123 
Goodspeed,  Arthur,  222 
Gramme,  101 
Grenet,  52 

Grove,  Sir  William  Robert,  45 
Guericke,  Otto  von,  34 

Hedley,  W.  S.,  181 
Herz,  114,  116 
Hirschmann,  148 
Hittorf,  210 
Holtz,  40 
Houston,  E.  J.,  105 

Jewell,  152 

Kellogg,  J.  H.,  198 
Kennelly,  A.  E.,  105,  180,  199 


Kirchhof,  Gustav  Robert,  65 
Kleist,  44 

Leclanche,  54 
Lenard,  210 
Leonard,  C.  L.,  223 

Mascart,  134 
Meyrowitz,  E.  B.,  208 
Morton,  W.  J.,  116,  130,  132 

Neef,  192  . 

Noe,  F.,  103 

Ohm,  George  Simon,  62 
Queen,  215 

Ramsden,  Jesse,  35 

Remak,  R.,  137 

Rontgen,  William  Konrad,  2IO 

Rudisch,  J.,  139,  144 

Smee,  51 
Stoehrer,  138 
Sweet,  W.  M.,  223 
Symmer,  23 

Tesla,  Nikola,  116 
Thompson,  Sir  William,  45,  115 
Thomson,  Elihu,  116 
Toepler,  42 

Vetter,  J.  C.,  145 

Volta,  Count  Alessandro,  36,  45 

Von  Ziemssen,  H.,  156,  196 

Wagner,  R.  V.,  192 
Waite  and  Bartlett,  122 
Wappler,  159,  161,  169,  209 
Watteville,  A.  de,  155,  156 
Weston,  85,  89,  162 
Wheatstone,  Sir  Charles,  93 
Wimshurst,  41 


229 


INDEX  TO  BOOK  I 


ACCUMULATORS,  206 

Acids  as  anions,  73 

Air-breaking  wheel  for   X-ray  apparatus, 

214 

Alkalies  as  kations,  73 
Alternating  currents,   105,   108,  179,   181, 

184,  185,  215 

electromotive  force,  105,  108 
induced  current,  104 
Alternations,  voltaic,  109,  154 
Alternator,  dynamo,  101 

for  electrotherapeutic  purposes, 

Kennelly's,  199 
Amalgamation  of  zinc,  52,  53 
Ammeter,  83 

principle  of,  84 

use  of,  to  determine  unknown 

resistance,  94 
Weston's,  85 
Ammonium  chlorid,  53 
Ampere,  the,  as  measure  of  current,  77 
as  measure  of  quantity,  63 
as  measure  of  strength,  63 
as  unit  of  current,  63 
compared  and  defined,  64 
Ampere-hour,  63 
Amperemeters,  83 
Ampere's  rule  for  deflection  of  magnetic 

needle,  73 
Anion,  the,  72 
Anode,  57 

in  electrolysis,  73 

Antikathode  as  the  source  of  X-rays,  213 
Antimony,  57 

and  bismuth  couple,  102 
electropositive  in  thermic  series, 

103 
Apparatus,  accessory,  136 

electric,  for  diagnosis  and  ther- 

apeusis,  171 
faradic,  99,  191 

normal,  197 
portable,  198 

for  altering  electromotive  force, 
190 


Apparatus  for   exciting  current  for  X-ray 

production,  216 
for  hydro-electric  baths,  202 
for  Rontgen  rays,  210 
frictional,  34,  120 
galvanic,  46,  136 
high  frequency,  201 
localization,  for  X-rays,  223 
sinusoidal,  198 
volta  induction,  99,  191 

Arc,  voltaic,  31 

Arrangement  of  cells,  68 

Astatic  galvanometer,  8 1 

system  of  magnetized  needles,  80 

Attraction,  electric,  24 

of  light  bodies,  28 


BARIUM  platinocyanid,  219 
Bases  as  kations,  73 
Bath,  anodal,  2O2 
dipolar,  203 

galvanic  current  water,  202 
kathodal,  2O2 
monopolar,  202 

Baths,  hydro-electric,  apparatus  for,  202 
current  supply  for, 

203 
Batteries  and  cells,  171 

galvanic,  principle  of,  56 
portable,  dry  cells  for,  174 

potassium      bichromate 

cells  for,  174 
requirements    of,     171, 

172,  173 
Stationary,  cells  for,  172 

requirements  of,  171, 

172 

storage,  charged  from  line,  206 
Battery,  care  of,  177 

cells,  arrangement  of,  for  greatest 

pressure,  68 
arrangement  of,  for  greatest 

volume,  70 
choice  of,  171,  173 


231 


232 


INDEX 


Battery,  constancy  of,  172 

disorder  in,  location  of,  177 
electromotive  force  of,  172 
requirements  of,  for  medical 

purposes,  137,  171 
storage,  206 
thermo-electric,  102 
Bichromate  cells,  51,  17-4 

for  cautery  purposes,  205 
Bismuth,  57 

and  antimony  couple,  102 
electronegative  in  thermic  series, 

103 

Brenner's  plug  selector,  138 
Bridge,  Wheatstone,  93 
Bullets,    presence     of,     determined     by 

fluoroscope,  220 
Bunsen  cell,  51 


CADMIUM,  57 
Calcium  chlorid,  125 

tungstate,  219 

Calculus,  localization  of,  by  X-rays,  223 
Calorific  effects  of  electric  current,  76 
Capacity,  electric,  29 
Carbon  electrodes,  1 66 

rheostats,  145,  151,  187 
Cataphoresis,  76 

Cautery,  bichromate  cells  best  for,  205 
central  station  current  for,  205 
electric,  76,  203 
electrodes,  205 
rotary  transformer  for,  205 
storage  battery  reliable  for,  206 
Cell,  bichromate,  51,  68,  174,  205 
Bunsen,  51,  68 
choice  of,  for  battery,  173 

for  faradaic  apparatus,  197 
Daniell,  48,  68,  172 
galvanic,  46 
gravity,  49 

unsuited  for   stationary  bat- 
teries, 173 

Grenet,  52,  172,  197 
Grove,  49,  68 
Law  telephone,  55 
Leclanche,  53,  68 

for    faradaic    apparatus, 

198 
for    stationary    batteries, 

1.73 

unsuited  for  portable  bat- 
teries, 173 

selector,  Brenner's,  138 
combined,  140 
crank,  137 
Gaiffe's,  14! 
plug,  138 


Cell   selector,  Remak's,  137 
rider,  138 

Rudisch  and  Jacoby's,  139 
Stoehrer's,  138 
selectors,  136 

advantages  of,  137 
silver  chlorid,  55 

for  small  portable  bat- 
teries, 174 
Smee's,  51 
voltaic,  46 
zinc  platinum,  51 

Cells,  arrangement  of,  electromotive  force 
modified  by,  68 
in  parallel,  70 
in  series,  69 
bichromate,  for  cautery,  205 

for  electrolysis,  175 
for    portable    batteries, 

174 

solutions  for,  51,  175 
chromic  acid,  51 
cleansing  of,  175 
double-fluid,  47 

dry,  55 

for  portable  batteries,  174 
unsuited  for  stationary  batteries, 

174 
electromotive  force  of  principal  types 

of,  68 
secondary  (storage)  for  utilizing  line 

current,  179 
single-fluid,  47,  51 
storage,  forms  of,  206 

principles  of,  206 
Charge  of  electricity,  29 
Charging,  30 

by  influence,  27 

Chemical  action  in  production  of  electro- 
motive force,  33 

decomposition  by  electricity,  72 
effects  of  electric  currents,  72 
Chromic  acid  cells,  5 1 
Circuit,  branch,  resistance  in,  65 

breaker  or  interrupter,  191 
deflecting,  73 
divided,  6l,  65 
electric,  60 

magnetic  properties  of,  75 
resistance  of,  external,  69 
shunt,  66 

current  strength  in,  67 
simple,  61 
Circuits,  compound,  65 

current  strength   in   branches   of, 

65 

Kirchhofs  law  for,  65 
resistance  in  branches  of,  65 
variation  of  current  in  branches  of, 

66 


INDEX 


233 


Coil,  Dubois-Reymond,  194 

standard,  197 
induction,  97 

for  X-rays,  217 

Herz'  s,  for  high  frequency 

oscillations,  116 
induced  wire  of,  97 
inducting  wire  of,  97 
proper     construction     of, 

193 

primary,  99 

construction  of,  191 
Ruhmkorff,  for  high   frequency  cur- 
rents, 200 

for  X-ray  production,  217 
secondary,  99 

construction  of,  193 
Coils,  faradaic,  controller  for,  209 

standard,  197 
resistance,  principles  of,  90 

use  of,  as  rheostats,  143 
use  of,  in  measurements, 

91 

Collector,  lot 

Combiner,  gal vano- faradaic,  155 
Commutator,  IOI,  153 
Compound  circuits,  65 

shunt  circuit,  186,  189 
Conceptions,  fundamental,  17 
Condensation  of  electricity,  32 
Condenser   for    Ruhmkorff  coil   in   X-ray 

production,  217 
Condensers,  43 
Conducting  cords,  170 

location     of    break    in, 

I78 

wire    compared    with    water- 
pipe,  64 
Conduction,  21 
Conductors   and  insulators,  21 

and  resistances,  table  of,  59 
in  parallel,  resistance  dimin- 
ished by,  65 
in  series,  resistance  increased 

by,  65 

Constant  or  galvanic  current,  47 
Contact,  disordered,  location  of,  178 
electrification  by,  19,  22,  24 
Continuous  electromotive  force,  105 
Control,  importance  of,  as  a  factor  in  use  of 

dynamic  electricity,  136 
Controller  for  small  lamps,  faradaic  cells, 

and  small  motors,  208 
Controlling  apparatus,   136 

for  use  with  street  currents,  184, 

1 86,  1 88 

Copper   electronegative   to    zinc,    electro- 
positive to  carbon,  57 
in  thermic  series,  103 
Cords,   conducting,  170 


Coulomb,  the,  63 

the,  compared  with  gallon,  64 
Couple,  thermo-electric,   102 

voltaic,  47 

Crank  cell  selector,  137 
Crookes  tube,  212 
Current,  alternating,  105,   108,  179 

dynamo,    control    of, 
for     medical     pur- 
poses, 179,  184 
dynamo,  cut-outs  for, 

184,  185 
dynamo,    dangers  of, 

181,  184,   185 
induced,  104 
interrupted,  103 
X-ray  tube  for,  215 
battery,  control  of,  136 

requirements  of,  172 
character  of,  dependent  on  char- 
acter of  electromotive  force,  113 
closure  induction,  96 
combiners,  155 
constancy  of,  172 
constant,  47 
continuous,  105 
control  of,  136 
controller,  149 
deflecting,  73 
direct  dynamo,  IOI,  179 

dynamo,  as  constant  cur- 
rent for  physician's  use, 
179 

dynamo,  as  inducing  cur- 
rent for  faradaic  coils, 
198 

dynamo,     control    of,    for 
medical    purposes,   184, 
1 86 
dynamo,  dangers  of,   1 80, 

181,  185 

dynamo,  distribution  of,  by 

three-wire   system,  181 

dynamo,  regulation  of,  180 

dynamo,  regulation   of,  by 

author's  method,  188 
direction,  29,  56,  57,  73,  108 
dissymmetric  alternating,  105,  1 1 1 
double  shunt,  189 
dynamic,  45 
Edison  direct,  179 
Edison  direct,  voltage  of,  181 
electric,  29,  32,  47 

calorific  effects  of,  76 
chemical  effects  of,  72 
circuit  of,  59 
compared  with  water,  64 
diminution  of,  by  increas- 
ed resistance,  65 
dynamic  effects  of,  76 


234 


INDEX 


Current,  electric,  effects  of,  72 

magnetic  effects  of,  73 
magnetic  field  of,  73 
measurement  of,  77 
mechanical  effects  of,  76 
origin  of,  32, 
polarization  effects  of,  73 
pressure  of,  33,  62,  64 
production  of,  33 
variation   of,  in  branches 
ofcompoundcircuits,62 
varieties  of,  33,  105 
exciting,  for  high  frequency  oscil- 
lations, 201 
for  induction  apparatus, 

197 

for  X-rays,  216 
extra  induced,  98 
faradaic,  95 

apparatus  for,    99,  190, 

197 
apparatus  for,  principles 

of,  191 
measurement    of,     195, 

197 

type  of,  191 
franklinic,  120 

apparatus  for,  134 
characteristics  of,  134 
methods  of  using,  126 
polarity  of,  134 
type  of,  112 
voltage  of,  134 
from  cells  in  parallel,  formula  for, 

7* 

in  series,  formula  for,  69 
galvanic,  47 

apparatus  for,  136 
effects  of,  72 
measurement  of,  156 
polarity  of,  176 
regulation  of,  136,  141, 

149,  15°,  IS2 
galvano-faradaic,  155 
greatest,  rule  for,  71 

volume   of,   arrangement 

of  cells  for,  70 
high  frequency,  113 

apparatus  for,  200 
isochronous      os- 
cillations of,  114 
use   of,  by  auto- 
conduction,  201 
use  of,  by  conden- 
sation, 202 
use  of,  by  shunt- 
ing, 201 

increase  of,  by  diminution  of  re- 
sistance, 65 
sudden,  danger  of, 1 85 


Current,  induced  dynamic,  95 

apparatus   for, 

99,  I91 
m  e  a  surement 

of,  195 
regulation    of, 

195 

intermittent,  105,  108 
interrupter,  153 
in  the  cell,  direction  of,  56 
in  the  wire,  direction  of,  57 
lighting,  dangers  of,  1 80 
magnetic,  185 

magneto-induction,   97,    loo,    190 
measurement  of,  62,  73,  77,  156, 

195 

of  water,  64 
opening  induction,  96 
oscillatory,  113 

pressure,  measurement  of,  63,  86 
proportional  to  number 

of  cells,  137 
regulation  of,  137,  142, 

149,  150 

primary,  for  induction,  96 
pulsating,  105 
pulsatory,  107,  112 
reduction    by  lamps    dangerous, 

187 
regulation,  136,  180,  195 

by  cell  selectors,  137 
by  change  of  voltage, 

149 

by    resistance  in  cir- 
cuit, 150,  152,  1 80 
by  resistance  in  shunt, 
142,  151,  152,  153, 
I 68,  188 
by  rheostat,  141,  152, 

153 

compound    or  double 
shunt   method      of, 
185,  186,  188 
principles  of,  149 
reverser,  109,  153 
self-induction,  194 
shunt,    reduced   by   second    con- 
troller, 189 
sinusoidal,  104,  105,  112 

apparatus  for,  198 
static  induced,  115,  132,  133 
steady,  104,  179,  186 
street,    carbon    rheostats    unsatis- 
factory with,  187 
strength,  measurement  of,  63,  73, 

77,  156,  195 
of  induction,  195 
regulation   of,    64,    66, 

136,  1 80,  1 86,  195 
unit  of,  63 


INDEX 


235 


Current  supply,  sources  of,   120,  136,  171 
for      cautery, 

205,  206 
for       faradaic 
a  p  paratus, 
197 

for  hydroelec- 
tric   baths, 
203 
for     Rontgen 

rays,  216 
for     small 
lamps,   208 

symmetric  alternating,  105,  III 
thermo-electric,  IOI 
transformed,     system    of,     danger 

from,  184 
unit,  63 

variation,  law  of,  62 
variation  of,  in  branches  of  com- 
pound circuit,  66 
Currents,  battery,  regulation  of,  136 

regulation    of.   by    rheo- 
stat, 142,    152 
branch,    strength  of,    in  divided 

circuits,  65 
central  station,  utilization  of,  in 

medicine,  178,  186,  188 
dynamo,  179,  1 86 
electric,  acted  on  by  magnets,  76 
action  of,  on  magnets,  76 
reciprocal  actions  of,  76 
leakage,  danger  from,  i8l 
momentary,  47,  96,  97 
polarization,  in  animal  tissue,  73 

in  cells,  48 
varieties  of,  105 

Cut-outs  and  lamps,  fusible,  185 
Cylinder  machine,  36 

Glaeser's,  123 
Cylindric  inductor,  IOI 


DAMPER,  use  of,  with  faradaic  coil,  195 

Damping  of  galvanometer,  83 

Danger   from     breakdown     of    insulation, 

184 

from  leakage  currents,  182 
from  sudden  increase  of  current, 

185 
Dangers  in  use  of  light  and  power  currents, 

1 80 

Dead  beat  galvanometer,  83 
Decomposition,  chemical,    by     electricity, 

72 

Deflecting  circuit,  73 

Deflection  of  needle  by  galvanic   current, 
73 


Density  of  electricity,  24 
Depolarizing  cells,  50 

material,  53 
mixture,   54,  55 
Dielectric,  31 

Differential  galvanometer,  83 
Direct  current  machine,  IOI 

spark,  127 
Discharge,   complete,  30 

conductive,  31,  32 
convective,  31 
disruptive,  31 
oscillatory,  113 
partial,  30 
Discharging,  30 

Distance,  effect  of  electricity  at  a,  23 
Distribution  of  electricity,  24 
Dry  cells,  55 

for  portable  batteries,  174 
Dubois-Reymond  coil,  194,  197 

standard  sled   apparatus 
for   measurement     of 
faradaic  currents,  197 
Dynamic  effects  of  electric  current,  72  76 
electricity,  45 
induction,  76 
Dynamo  currents,  medical  use  of,  lor,  179 


E 

Earth,  currents,  danger  from,  182 

the,  a  reservoir  of  electricity,  22 
the,  zero  potential  of,  29 
Edelmann's  faradimeter,  196 
Edison  adjustable  vacuum  tube  for  X-rays, 

214 

current  in  New  York,  179 
instantaneous  air-breaking   wheel, 

218 

Effects  of  electric  currents,  72 
Electric  apparatus,  kinds  of,  119 
cautery,  119,  203 
circuit,  the,  47,  60 
current,  47 

compared,  64 
defined,  64 
equilibrium,  28 
fluid,  21 
light,  119 

current,  use  of,  for  medical 

purposes,  1 80 

lighting  lamp  for  medical  explora- 
tion, 207 
spark,  31 

localization  of   130 
spray,  31 
state,  19 
units,  62 

compared  with  water,  63 


236 


INDEX 


Electric  vibrations,  17 

Electrical  Congress,  International,  197 

Electricity,  21 

chemical  decomposition  by,  72 

condensation  of,  32 

density  of,  24 

distribution  of,  24 

dynamic,  45 

flow  of,  compared  with  water, 
29 

frictional,  22,  34,  120,  126 

galvanic,  medical  use  of,  22,  136 

in  motion,  64 

magneto-,  22 

nature  of,  17 

produced   by   chemical   action, 

33,  45 

produced  by  contact,  33,  45 
produced  by  friction,  34 
produced  by  heat,  24,  33,  101 
produced  by  magnetization,  97 
quantity  of,  in  charged   body, 

29 
static,  34 

medical  use  of,  1 20 
methods    of    application 

of,  126 

thermo-,  22,  24,  33,  101 
unity  of,  22 
Electrification,  20 

by  calorific  action,  24 
by  contact,  20,  24 
by  fri  tion,  19,  22,  34 
by  influence,  26 
by  mechanical  action,  24 
methods  of,  22 
negative,  23 
phenomena  of,  20 
polarity  of,  23 
positive,  23 

Electrocautery,  119,  203 
Electrode,    ball,   127 

concentrator,  132 
directing,  for  spark,  130 
handle,  163 

combination,  168 
current-controlling,  169 
detachable,  167 
interrupting,  169 
pole-changing,  169 
metal  cap,  131 
Morton's  pistol,  134 
spark,  131 
roller,  130 
unpolarizable,  167 
wire  brush,  1 66 
with  elastic  belt,  169 
with  hard- rubber  spring,  169 
wooden  ball,  127 
Electrodes,  construction  of,  162 


Electrodes,  coverings  for,  166 

for  galvanic  current,  162 
for  static  machine,  125 
moistening  of,  177 
Electrodiagnosis,  apparatus  for,  171 
Electrodynamic  induction,  96 
Electrolysis,  72,  77,  175 
Electrolyte  in  electrolysis,  72,  78 

of  cell,  47 

Electrolytes  for  bichromate  cells,  175 
Electrolytic  action    on    surface  of  human 

body,  167 
laws,  78 

measurement  of  current,  77 
Electromagnetic  induction,  97 

induction  apparatus,  191 
measurement,  73,  78 
Electromagnetism,  73 
Electromagnets,  75 
Electromedical  battery,  137 
Electrometer,  29 
Electromotive  force,  30,  33,  46 

alteration  of,  33, 68, 95 
alteration  of,  appara- 
tus for,  190 
alternating,    105,    108 
alternating  d  i  s  s  y  m  - 

metric,  105,  HI 
alternating,      graphic 
representations    of, 

IO9,   HO,    111,112 

alternating  symmet- 
ric, 105,  III 

as  pressure,  33,  64 
.       compared,  57,  64 

continuous,  105 

continuous,  graphic 
representations  of, 
1 06 

direction  of,  1 06 

dissymmetric  alternat- 
ing, III 

dissymmetric,  graphic 
representation  of, 
112 

dissymmetric,  waves 
of,  HI 

due  to  difference  in 
potential,  32 

gradually  alternating, 
graphic  representa- 
tion of,  109 

greatest,  arrangement 
of  cells  for,  68 

intermittent,  108 

intermittent,  graphic 
representation  of, 
1 08 

law  of,  62 

measurement  of,  77 


INDEX 


237 


Electromotive  force,  modification  of,  by  ar- 
rangement of  cells, 
68 

negative,  106 
of  various  cells,  68 
origin  of,  30 
positive,  1 06 
produced   by  friction, 

112 

production  of,  33 
pulsating,    105,     107, 

"3 

pulsatory,graphic  rep- 
resentation of,  113 

relation  of,  to  current, 
62,  63 

relation  of,  to  elec- 
tricity, 33 

sinusoidal,  104,  105, 
112 

sinusoidal,  graphic 
representation  of, 
112 

steady,  104 

symmetric,  105,  III 

symmetric,  graphic 
representation  of, 

III,    112 

symmetric,   waves  of, 

in 
tension, potential,  and, 

33 

unit  of,  63 
variations  in, causes  of, 

J°5 
varieties  of,  105 

series,  galvanic,  57 

thermo-electric,  103 
Electronegative    substances    of    relatively 

low  potential,  57 
Electrophorus,  36 
Electrophysics,  17 
Electropoion  fluid,  53 
Electropositive     substances    of    relatively 

high  potential,  57 
Electroscope,  28 
Element,  thermo-electric,  IO 
Elements,  voltaic,  47 
Engelmann'  s  segmentary  rotary  interrupter, 

193 

Equalization  of  potentials,  31,  32,  47 
Equilibrium,  electric,  28 

disturbance  of,  30 
restoration  of,  by  con- 
duction,  32 
restoration  of,  by  dis- 
charge, 31 

Excitation,   electric,    20 
Exploring  lamp,  207 
Eye,  localization  of  foreign  bodies  in,  223 


Faradaic  coil,  191 

current,  155,  190,  195 
Faraday's  magneto-electric    machine,    loo 
Faradimeter,  Edelmann's,  196 
Fluid,  electric,  21 

electropoion,  53 
rheostats,  147 
Fluids,  exciting.  47 
Fluorescent  light  from  X-ray  excitation,  21 1 

screen,  219 
Fluoroscope,  218 

uses  of,  220 

Focusing  tubes  for  X-rays,  213 
Force,  electromotive,  varieties  of,  32,  46, 

57,  105 
Foreign  bodies,  localization  of,  by  X-rays, 

220 
Formula  for  cells  in  parallel,  71 

in  series,  69 
of  electric  capacity,  30 
Ohm's,  62 
Franklin  plate,  43 
Frank!  inic  current,  134 
Franklin's  one-fluid  theory,  23 
Friction,  electrification  by,  19,  22 

electromotive  force  produced  by, 

character  of,  112 
machines,  34,  120 

attachments  for,  125 
care  of,  125 
charging,  124 
poles  of,  differentiated, 

135 
spark,  31 

applications  of,  130 
Frictional  electricity,  22,  34 

applications  of,    126 
Fulminating  pane,  43 
Fusible  cut-outs  and  lamps,  185 


GAIFFE'S  cell  selector,  141 
Galvanic  apparatus,  136 
cell,  46 
controller,  187 
current,  47 

effects  of,  72 
water-bath,  2O2 
electricity,  22 
Galvanocautery,  76,  203 
Galvano-faradaic  combiner,  154 
Galvanometer,  60 

astatic,  8 1 
construction  of,  78 
damping  of,  83 
differential,  83 
Edelmann's,  156 


238 


INDEX 


Galvanometer,  horizontal,  156,  161 
mirror,  81 
principle  of,  7.1 
unit,  156 
vertical,  156 

Geissler  tube,  212 

Glaeser's  cylinder  machine,  123 

Gold,  57 

Gold-leaf  electroscope,  28 

Gramme  ring  inductor,  101 

Graphite,  57 

rheostat,  modified,  145 
Rudisch's,  144 

Gravity  cells,  49,  173 

Grenetcell,  52,  172,  197 

Grove  cell,  49,  68 


H 

HEAT,  generation  of,  in  rheostats,  187 

in  production  of  electromotive  force, 

33,  ioi 

Heating  effects  of  current,  law  of,  76 
Herz,  experiments  of,  114 
Herz's  induction  coil,  116 
High  frequency,  currents  of,  113 
Hirschmann's  fluid  rheostat,  148 
Hoi tz  machine,  40,  120,  125 
Holtz-Toepler  machine,  42 

principles,  122 
Horseshoe  inductor,  100 
Hydrogen  in  electrolysis,  72 


INCANDESCENCE,  electric,  cause  of,  76 
Indirect  spark,  127 
Induction,  26,  95 

apparatus,  190 

control     of     current 

from,  195 
dynamic,  191 
exciting  current  for, 

197 

magneto-electric,  191 
mechanical,  190 
standard,  197 
voltaic,  19! 
coil,  operation    of,    for  X-ray, 

217 

coils,  97,  191,  193,  197 
dynamic,  76 
machine,  40,  41,  120 
magnetic,  95,  190 
magnetic  and  voltaic,  combina- 
tion of,  98,  191 
static,  26,  1 20 
voltaic,  96,  191 


Inductors,  101 

Influence,  charging  by,  27 

electrification  by,  26 
machines,  40,  120 

care  of,  125 
charging  and  loss   of 

charge  in,  124 
Insulated  platform,  125 
Insulation,  22 

static,  131 
Insulators,  21,  59 
Intensity  of    the  thermo-current,    law   of, 

103 

Intermittent  electromotive  force,  108 
Internal  resistance  of  cell,   48 

of  circuit,  59 

International  Electrical  Congress,  197 
Ions  in  electrolysis,  72 
Iron,  57,  103 


JACOBY  and  Rudisch's  cell  selector,  140 
Jacoby's  electrode  handle,  168 

method  of  regulation   of  dynamo 
current,  188 


K 

KATHODE,  57 

in  electrolysis,  73 
rays,  211 

concentration  of,  213 
deflection  of,  212 
nature  of,  212 
Kation,  the,  72 

Kirchhof  s  law  of  divided  currents,  65 
Kleist  jar,  44 


LAMP  as  limit  resistance,  1 86 

electric,  currents  employed  for,  179, 

181 

exploring,  207 

for  use  of  reflected  light,  208 
small,  controller  for,  209 
unsuited  for  control  of  current,  185, 

187 
Law  of  electromotive  force,  62 

of  Kirchhof  of  divided  currents,  65 
of  thermogenesis  in  a  circuit,  76 
Ohm's,  of  relationship  between  cur- 
rent, electromotive  force,  and  re- 
sistance, 62 

Law  telephone  cell,  55 
Laws,  electrolytic,  78 
Lead,  57,  103 
Leclanche  cell,  53,  68,  172,  173,  198 


INDEX 


239 


Lesions,  surgical,   determined   by   fluoro- 

scope,  220 
Leyden  jar,  44,  126 

spark,  129,  130 
Light,  electric,  119,  207 
Lighting,  electric,  76,  179 
Lightning,  31 
Limit  resistance,  184,  1 86 
Lines  of  magnetic  force,  75 
Localization  of  electric  spark,  130 

with  X-rays,  22O 
Loss  of  charge  and  recharging  machine, 

124 

M 

MACHINE,     Faraday's     magneto-electric, 

100,  191 

friction,  .Bose's,  34 
cylinder,  36 
Guericke's,  34 
Hawksbee's,  34 
plate,  35 
Ramsden's,  36 
Holtz,  40,  1 20,  124 
Holtz-Toepler,  42,  122 
induction,  40,  I2O 
influence,  40,  1 20 

attachments  for,  1 25 
care  of,  125 
charging,  124 
magneto-induction,  191 
mica-plate,  42 
volta-induction,  191 
Wimshurst,  41,  124 
Magnetic  action,  measurement  by,  78 
effects  of  electric  current,  72 

of  the  galvanic  current,  73 
field  of  the  galvanic  current,  73, 

75 

induction,  95 
meridian,  73 

needle  deflected  by  galvanic  cur- 
rent, 73 

Magnetized  needles,  79 
Magneto-  and  volta-induction,  combination 

of,  98 

Magneto-electric  machine,  Faraday's,  loo 
or  rotary  apparatus,  190 
Magneto-electricity,  22 
Magneto-induction,  97 
Magnets  acted  upon  by  electric  currents,  76 
action  of,  upon  electric  currents,  76 
Manganese  peroxid,  53 
Massage,  static,  130 
Measurement  by  magnetic  action,  78 
electric,  units  of,  62 
electrolytic,  77 
of  current  strength,  83,  156, 
195 


Measurement  of  electric  currents,  77 

of  pressure,  87 

of  resistance,  90 
Measuring  instruments,  77 
Mechanical  effects  of  electric  currents,  72, 

75 

energy  in  production  of  elec- 
tromotive force,  33 
induction  apparatus,  190 
Mercury,  57,  103 
Milliampere,  the,  63 
Milliamperemeter,  aperiodic  horizontal,  of 

Eulenburg,  160 
division  of  scale  of,  157 
for  diagnostic  and  ther- 
apeutic use,  construc- 
tion of,  157 
practical  choice  of,  1 60 
upright,  159 
Wappler,  159 
Millimeter  scale,  196 
Mirror  galvanometer,  8 1 
Molar  effects  of  electric  current,  76 
Molecular  effects  of  electric  current,  76 
Morton's  spark  electrode,  130 
Motion,  molecular,  17 
Motor,  electric,  loi 
Multiplicator,  principle  of,  79 


N 

NEEDLE,  magnetic,  73 

Neef  or  Wagner  hammer,  192 

Negative  electrification,  23 

electromotive  force,  106 

plate,  the,  57 

pole,  the,  57 
Nickel,  57.  103 
Noe  thermobattery,  103 
Nonconductors,  21 


OHM,  the  measure  of  resistance,  77 
the  unit  of  resistance,  62,  64 
Ohm's  law,  63 
Oscillations,  electric,  compared,  114 

isochronous,  114 
Osmosis,  electric,  76 
Oxygen  in  electrolysis,  75 


PAIR,  voltaic,  47 

Physical  effects  of  electric  currents,  72 

Physiologic  effects  of  electric  currents,  72 

Pile,  voltaic,  45 

Plate,  battery,  57 


240 


INDEX 


Plate,  battery,  negative,  47,  56,  57 
positive,  47,  56,  57 
Plates,  battery,  47,  56 
Platinum,  57,  103 
Plug  cell  selector,  Brenner's,  138 
Polarity  of  electrode  tested  by  taste,  177 
of  static  machines,tests  for,  134, 

»3S 

tests  for,  175 

Polarization  currents  in  animal  tissue,  73 
effects  of  electric  current,  73 
in  voltaic  cells,  48 
Pole  tester,  176 
Poles,  battery,  57 

of  friction   machine    differentiated, 

»35 

Positive  battery  plates,  47,  56,  57 
electrification,  23 
electromotive  force,  106 
pole  of  battery,  57 
potential,  29 
Potential,  29 

difference  of,  as  cause  of  electric 

pressure,  58 
difference    of,     from    chemical 

action,  46 
differentiated  from  quantity, 

29 

equalization  of,  32,  47,  58 
negative,  29 
positive,  29 
relation     of,     to     electromotive 

force,  33 

relation  of,  to  tension,  33 
Pressure,  electric,  57 

cause  of,  58 

compared    with    water, 

57,  64 

measurement     of,     by 
comparative    method, 

87 

measurement  of,  by  dif- 
ferential method,  87 
unit  of,  63,  64 
of  battery  current  proportional 

to  number  of  cells,  137 
of  water,  57,  58 
Primary  coil,  function  of,  191 
Pulsatory  electromotive  force,  107 

electromotive  force  produced  by 
friction,  1 12 


QUANTITY  or  charge,  29 

or    charge   differentiated  from 
potential,  29 

unit  of,  63 
Quantum,  normal   of  electricity,  23 


RADIOGRAPHIC  table,  223 
Rays,  actinic,  19 

kathode,  211 

concentration  of,  213 
deflection  of,  212 
nature  of,  212 
luminous,  19 
Rontgen,  19,  210 
thermic,  19 
X-,   19,  211 
Recharging  machine  and  loss    of  charge, 

124 
Regulation  of  battery  currents,    137,    142, 

152 

of  central  station  currents,   186 
of  current  by  cell  selectors,  137 
of  current  by   change    of  vol- 
tage, 149 
of  current  by  compound  shunt, 

186,  188 

of  current  by  resistance   in  cir- 
cuit, 142,  150 
of  current    by     resistance     in 

shunt,  142,  152,  186,   188 
of  current  by  rheostat,  141 
of  current    strength,    principle 

of,  67 
Repulsion,  electric,  24 

of  light  bodies,   28 
Resistance,  23,  60 
coils,  90 
comparison    of,     with    water 

flow,  58 

device,  metal,  with  sufficient 
heat-radiating  surface  for 
control  of  street  currents, 
188 

external,  59,  69,  70,  71 
in  parallel,  61,  65 
in  series,    60,  65,    142,    186, 

188 
in  shunt,    65,    66,     67,    142, 

186,  188 

internal,  48,  59,  69,  70,  71 
law  of,  60,  62 
limit  in    control    of    dynamo 

currents,  186,  187,  188 
measurement  of,  90 
path    of  least,    in   compound 

circuit,  67 
regulation  of  current  by,  142, 

1 86 

relation  of,  to  temperature,  68 
total,  of  a  circuit,  69 
unit  of,  62,  64 

unknown,  determined  by  am- 
meter and  voltmeter, 
94 


INDEX 


24I 


Resistance,  unknown,  determined  by  sub- 
stitution, 91 
determined  by 
Wheatstone 
bridge,  93 

variability  of,    in  a  circuit,  68 
variable,  in  current,  142 
wire,  trustworthy   for  control- 
ling street  current,  187 
Resistances,  table  of  conductors  and,  59 
Rheostat,  141 

carbon,  Vetter's,  145 
fluid,  147 

Hirschmann's  improved,  148 
for  primary  current  of  faradaic 

coil,  198 
graphite,  modified,  145 

Rudisch's,    144 

metal,  with  sufficient   heat-radi- 
ating surface,  187 
method  of  using,  153 
regulation   of  current  by,    141, 

152,  182,  184,  187,  198 
use  of,  151,  153 

of,  with  battery  current,  152 
of,  with  street  current,   182, 

184,  187 
water,  150 
wire,  143,  187 
Rheostats,  carbon,  unsatisfactory  with  street 

currents,    187 
use  of,  151 

choice  and  use  of,  148 
correct  connection  of,   115,  184 
wire,  for  measuringpurposes,  143 
Rider  cell  selector,  Stoehrer's,  138 
Roller  electrode  for  applying  friction  spark, 

130 
Rontgen  rays,  119,  210 

apparatus  for,  212,  21 6,  217 
characteristics  of,  210 
concentration  of,  213 
dermatitis  from,  226 
exciting  current  for,  216 
fluorescence  from,  210,  218 
fluoroscopy  by,  219 
localization     apparatus    for 

examination  by,  223 
skiagraphy  by,  220 
source  of,  213 
tubes  for,  213,  214,  215 
Rotary  transformer,  205 
Rudisch's  cell  selector,  139 

rheostat,  144 
Ruhmkorff  coil  for  high  frequency  currents, 

200 

for  Rontgen  rays,  2 1 6 
Rule,  Ampere's,  for  deflection  of  needle  by 

electric  current,   73 
for  greatest  battery  current,  71 
16 


S 


SCALE,  milliamperemeter,  division  of,  157 
Series,  cells  arranged  in,  69 

conducting  wires  in,  69 
electromotive,  57,  103 
multiple,  cells  in,  71 
resistance  in,  61,  187 
thermo-electric,  103 
Shunt  circuit,  66 

compound,  186 

in  galvanometers,  83 

in  milliamperemeters,  157 

principle  of,  as  applied  to  electricity, 

67 

principle  of,  as  applied  to  water,  66 
principle,     regulation     of    current 

strength  by,  67,  142,  187 
rheostat  placed  in,  153 
therapeutic  current  derived  from,  187 
Shunts,  65 

division  of  current  in,  65 
Silver,  57,  103 
Silver-chlorid  cell,  55 

for  portable  battery,  174 
Single-fluid  cells,  47,  51,  55 
Sinusoidal  apparatus,  98 

current,  104,  105,  112 
electromotive  force,  112 
Skiagrams,  210,  221 
Skiagraphy,  22O 
Smee's  cell,  51 

Solenoid,    oscillations    in,    for    high    fre- 
quency current,  2OI 
Solution,  potassium  bichromate,  formula  of, 

53 
Spark,  direct,  127 

method  of  applying,  129 
electric,  31 

localization  of,  130 
electrode,  Morton's,  130    ' 
friction,  130 
indirect,  127 

method  of  applying,  128 
static,  31,  113,  127 
Spectrum,  solar,  18 
Spray,  electric,  31 
Standard  faradaic  apparatus,  197 

units,  62 
State,  electric,  19 
Static  breeze,  131 
electricity,  34 

medical  use  of,  1 2O 
methods    of    application 

of,  126 
induced  current,  115,  132 

method      of    pro- 
ducing, 133 
insulation,  127,  131 
machine,  discharge  of,  113 


242 


INDEX. 


Static  machine  for  X-ray  current,  216 
machines,  40,  120 
massage,  130 

Storage  batteries,  charging  of,  206 
battery  for  cautery,  206 
cells,  206 
Surface,  application  of  electricity  to,  167 

electrification,  25 
Symmer,  theory  of,  23 
Symmetric  alternating  electromotive  force, 
III 


TABLE  of  conductors  and  resistances,  59 

Temperature  as  modifying  resistance,  68 

Temporary  magnet,  191 

Tension,  electric,  26,  33 

Theory,  double-fluid,  of  Symmer,  23 

one-fluid,  of  Franklin,  23 
Thermic  action  of  galvanic  current,  72,  "j6 
Thermocurrent  intensity,  law  of,  103 
Thermo-electric  battery,  102,  103 
couple,  1 02 
element,  IOI 
series,  103 

Thermo-electricity,  22,  33,  IOI 
Thermopile,  102 

for  excitation  of  current  with 

faradaic  coil,  198 
Noe's,  103 

Thompson's  theory  of  static  induced  cur- 
rents, 115 

Thorax,  examination  of,  by  fluoroscope,  220 
Thunder,  31 
Transillumination   by  means   of  Rontgen 

rays,  210 
Tubes,  focusing,  213 

with   adjustable  vacuum, 

213 

for  X-rays,  212 
high  vacuum,  of  Crookes,  212 
low  vacuum,  of  Geissler,  212 

U 

UNITS  of  electric  measurement,  62 

of  electric   measurement  compared 

with  water,  63 
Unity  of  electricity,  22 


VETTER  rheostat,  145 
Vibrations,  electric,  17 
Volt,  63,  64 

controllers,  136,  150 

the,  unit  of  electromotive  force,  64, 

77 

Voltage,  change  of,  as  means  of  regulating 
current,  149 


Voltage  of  battery,  regulators  for,  148 
of  dynamo  current,  181 
of  dynamo  current,  regulation  of, 

184,  1 86,  1 88 
of  franklinic  current,  134 
of  galvanic  current,  regulation  of, 

150,  161 
required  to  produce  any  current, 

64 
Voltaic  arc,  31 

couple,  47 
elements,  47 
induction,  95 
pair,  47 
pile,  45 

Volta-induced  current,  99 
Volta-induction  apparatus,  99,  191 
Volta-magnetic  apparatus,  190 
Voltameter,  72,  77 
Voltmeter,  Jewell,  162 

principle  of,  86 

use  of,  to  determine  unknown 

resistance.  94 
Weston's,  89,  162 
Voltmeters,  86 

W 

WAPPLER'S  milliamperemeters,  159 
Water,  current  of,  64 

electrolytic  decomposition  of,  72 
flow  of,  compared  with  electricity, 

29 

rheostat,  use  of,  150 
Weston  ammeter,  85 
voltmeter,  89 
Wheatstone  bridge,  93 
Wheel,  Edison,  instantaneous  air-breaking, 

218 

Wimshurst  machine,  42,  124 
Wire,  conducting,  6l,  64 

as  a  magnet,  73 
disorder  in,  178 
direction  of  current  in  the,  57 
resistance,  187 
rheostats,  143 


X-RAY  dermatitis,  226 
X-rays,  210 


ZERO  potential,  29 
Zinc,  46,  103 

amalgamation  of,  52 

electropositive,  57 

local  action  of,  in  cells,  52 
Zinc-carbon  cell,  51 
Zinc-platinum  cell,  51 


•  • 

?!*' 


Date  Due 


OF 

PATH'lC 
HSEOJ 


CAT.    NO.    23    233  PRINTED    IN    U.S.A. 


m  •'•Illl  IIIH  ll/j/  Hill  i II f| 


Book  No. 
Source__ 


WB300 
C6T8s 
1901 
v.l 
Cohen . 

A  system  of  physiologic 


WB300 
C6?8s 
1901 
v.l 
Cohen . 

A  system  of  physiologic 
therapeutics 


